1972 house with 174 sqm from the neighborhood

it’s annoying when you come into every topic with your hero story. No one asked how you feel about parents contributing something. Besides, has obviously also done quite a bit for the family without being paid for it. Sure, for you that’s a given...

But back to the topic: I’m missing the female factor a bit in the whole consideration. I understand that with such a fresh relationship you don’t immediately think about joint financing. But are you fundamentally agreed that she would also want to live there in the long run? Or do you already know that she won’t be the mother of your children?
If you are sufficiently sure about that, you can try the financing.
I would initially leave both the roof and the terrace out of the financing and calculate it as lean as possible for the bank.
If the roof is watertight after 50 years, it will last a few more years.
You can renovate the terrace yourself, you’re no stranger to handiwork, which to me strongly argues for keeping it.
The challenge will be to find a bank that values the house sufficiently in what is probably a structurally weak area to finance it. I guess it will be difficult without some additional equity.

Someone asked about the financing. And I didn’t start working part-time during my studies, so please pass the ball back to the OP. €3,000 for €420k is much too little in my opinion. In other threads, people with €4,500 household income and similar investments were advised against it.

Someone asked about the financing. And I didn't start working during my studies, so please pass the ball back to the OP.

Don't take it personally, I basically like your attitude and also appreciate people who really manage everything on their own instead of just inheriting and still whining. You just carried it around like a monstrance over several threads, so I had to comment on it.

€3,000 for €420k is far too little in my opinion. In other threads, people were advised against similar investments with a household income of €4,500.

However, there is a difference whether €3,000 is available for an individual or if a family of four has to live on it. As mentioned above, a person generally has between €1,300-1,500 considered in the household calculation by the bank. That leaves €1,500 for the house. Because of this and the theoretically very long possible term, it could work in terms of liquidity. I see the crux in the loan-to-value ratio. It won't be easy to get the financing.

I find the facts 3000€, sole earner, wrong timing, basically half-single, are reasons to consider whether to do it or not, or I can imagine that a bank would not make it feasible.

and a few 10,000€ reduce the interest by one or two tenths, we'll manage that. But I don’t assume we are talking about a very large amount (maybe 50-70?)

I also believe that although support from the parents can basically be accepted, it is not retirement provision for a few tenths of interest. Have you calculated how much you save? It’s nothing and thus one should keep the church in the village and leave the money to the parents. It’s too hot for nothing.

By the way, the parents’ money can also be used as a loan.

That’s how it is planned anyway. But you forget that this money also has to be paid back. And then I ask: from what, if the house also causes high additional costs. A 50-year-old house is a hobby both in terms of time and money. No big leaps are possible there. And under scrutiny is a young relationship on which this temporal and financial burden lies.

Now one could say that she, the woman, is not worth it if she doesn’t cooperate or support mentally. But is it fair to throw a young student into a responsible situation instead of going on short vacations, enjoying weekends carefree with a van, going out to eat, finding common hobbies and starting to build a nest together when the time comes?

Because of my situation – just finished studying, bought a car and put on some fat – I simply have no significant equity,

Nobody holds that against you, but precisely those are in my eyes reasons that the time is not right yet.

Buy the house now but hold back on renovation costs for now. Maybe your girlfriend will want to contribute to the renovation and (new) furnishing costs after she finishes her studies (in 2-3 years).

You come across as very down-to-earth and realistic, so in this case I would rather say: just go ahead. I would also accept money from the parents. It can be done as an interest-free loan with low repayments. I think the word retirement provision was unfortunately used. I hope that the parents only give money that is simply "left over" in case of doubt and that the parents themselves do not get into financial trouble. But I trust that all parties involved have that much sense.

You can do it as an interest-free loan with low repayment.

Yes, you can: (also leaving out the words age and retirement):
60000 loan from the parents, interest-free, … you also pay 500€ monthly, and that for 10 years. Or how long should the parents wait for their money?… I don't care, but it has to be mentioned.