We are beginning to plan the construction of our house

With all due respect, but this answer rather falls into the category "bending reality to one's own opinion."
It's quite interesting to spin this theory out of a few forum inquiries...

After my almost 2,000 forum posts, a direction is starting to emerge. Just read the threads "Financing feasible?" – then you will find many questions that go in the direction I outlined.

By the way, career and location are quite often combined, it is then called commuting... many people in Germany do that, regardless of age...

That's all fine, of course, but there are also enough couples who have realized that things don't work out as planned. Those who then had to sell the barely still affordable property they had on their hands, taking a loss...
It's about considering whether one really has to push the financial limits already in their early to mid-20s...
Nothing more and nothing less – this is not meant to be a general attack. If you can afford it, by all means do so – if not, maybe just dare to look beyond your own nose. Of course, when one's own house is so close, other things recede into the background. But this forum is good for that, since there are not only yes-men here but also critical comments.

It's about considering whether you really have to push your financial limits already in your early/mid 20s... Nothing more and nothing less - it’s not meant as a blanket attack.

Since I also still want to belong to the young people, I’ll explain how things have developed for us in recent years: We were sure early on (mid-20s) that we wanted to build a house. So, we acquired a plot of land and postponed the construction by 3-4 years. During this time, we continuously dealt with various house-building topics and have now landed with reality from our initial plan (a house for about 250,000€) at around 330,000€. The information on various ancillary costs and additional costs for KfW houses has also significantly improved, so everything around it has become more expensive. In fact, we will now have to finance about 100,000€ more than originally thought. I also thought in my mid-20s that I had plenty of knowledge about house-building costs and financing, but I was wrong. This has nothing to do with poor planning but rather that after years of dealing with a topic you simply know much more and can make more realistic assessments.

In short: This process that happened to us can lead to thinking in your mid-20s that you can afford a nice house (and once the dream has taken hold in your mind...), but reality looks different. Not necessarily that you can’t afford a house at all, but very likely not the house you have imagined in your mind.

Very briefly put: House-building costs are generally underestimated, and the effects are often more striking (nice word, haven’t used it in a while) for young people than for older people with more knowledge and experience.

What surprises me is why, in a forum about house building, inquiries from young people about the same lead to conclusions about the majority of all young people...

They don’t. I have been reading and moderating here for a while and read every post. I wouldn’t be a mod if I didn’t look at these inquiries critically: shared ownership requires more than love and some savings in the bank.

We often advise to wait, not to commit too early, and to still enjoy carefree life a bit longer. Unfortunately, carefreeness often changes with maturity over time... but also additionally or earlier due to external circumstances such as a shoebox apartment hanging on your heels that immobilizes you.
We are not mean-spirited nor do we boast about maturity.

There can be many reasons in favor of building a house at a young age:

Your arguments apply to people of all ages: the biggest obstacle is financing - one way or another.
I didn’t count them: but meanwhile there are inquiries here from aspiring builders who have not yet finished their training or have taken every small loan, so they are already burdened.
And here, age is indisputable: if a 40-year-old in retraining and without equity asks for advice regarding house building or financing, I give answers that can sometimes be unpleasant. Even if he’d love to have a house in the countryside, the interest rates are so low, and a bargain plot is being offered.

What speaks against building a house at a young age for me - spoken spontaneously:
1. What used to happen at 16 (starting to find one’s feet in a company) often happens nowadays only at 25 or even later. Correspondingly, personal development is delayed and stretches through the twenties. Often the career and one’s place in society must be earned over several years. This also includes local flexibility.
2. Many couples who found each other early and dream together of their own house often lose their commonalities over time because they still change so much when young—except for the mortgage and the children.
If both come together... ...! I know so many by now who have experienced point 2. Houses are nowadays sold, children grown up and partly relationship-wise disturbed because parents fooled them for years with the image of mutual fidelity and love, as there was still a shared house that caused high costs.

And no: I don’t belong to point 2.
And I know: some here recognize themselves or their fate.

Life plans are very diverse and one should not consider one’s own as a model example.. That is sometimes the problem of the older generation

Just imagine: the older generation live today as much as tomorrow and all generations live together in parallel – the older generation has an advantage: they have already experienced a lot. That is the beauty of a forum: the young person can benefit from the experience of the older (and not exactly the parents or relatives) – just as older people learn fresh expert knowledge from the young.
Often the problem of some younger people: they only see their young society and turn older people into the "generation of their parents" – and they are never right anyway.

ypg, there is practically nothing to add to that

So what do we learn from this, dear OP.. First, please check yourself and your loved one thoroughly to see if you really match.. Then ask your boss if your workplace is really truly secure.. And if you have planned the next few years and saved enough equity and no longer belong to the young generation that wants to compensate a hole in the ego with a big house... Then you may come back...everything else is far too dangerous and your life will end in divorce and financial ruin.. Howgh the forum has spoken... don't be afraid, they just want to play...

...or took out every small loan, so that they are already burdened now.
And here too, age is indisputable: if a 40-year-old in retraining and without equity asks for advice regarding building a house or financing, I give answers that can sometimes be unpleasant. Even if he so badly wants a house in the countryside, the interest rates are so low, and a bargain plot of land is being offered.

As a small addition, I feel that nowadays things are becoming more extreme. As soon as you turn 18 and earn your first money, the big car is bought on credit. Meanwhile, people watch Sky, listen to music on Spotify, and order through the Amazon Prime subscription because it’s cool. Nobody even realizes that the phone is also basically bought on credit with a 50-euro contract. What’s a small house compared to that? It doesn’t cost 300,000€, but only 700€ a month.
Young people are raised that way, and the (almost) free money doesn’t make it any better.
My parents still paid >8% for their home loan. They thought very carefully about whether they could afford it and how much equity they could bring in. This whole small loan and installment payment mentality didn’t exist back then, and that’s exactly why I generally assume that today’s 40-year-olds or older already approach financing more sensibly. (Of course, there are exceptions as always.)