Certainly not 30 years ago. Probably today, in the sense that there are only a few who already do this at that age. Like children in their early 20s. This is not a value judgment, but merely the observation that you are rather an exception.
30 years ago this was not the case, because career was never the top priority.
Nowadays, most people at 27 haven't even finished their studies yet... which is partly embarrassing. The focus of society in our generation is mostly somewhere else entirely.
However, there are also couples who do not focus on career and binge-drinking vacations until their mid-30s and perhaps have already achieved family and partnership goals in their mid-20s and may achieve in the coming years what some in their mid-30s can only dream of.
It always depends on the life situation and the priorities a couple sets.
OP: Please don’t let yourself be influenced. We are also laughed at because we are building a house at the end of our 20s and early/mid-20s here in the "village" – "small town" – and are clearly in the minority... But it’s a matter of attitude and always depends on how you as a couple set your goals.
And please consider whether 120m² without a basement is enough for you, that is really VERY small. At first, we were also on the line of: "120m² is fine," but with a basement, and we will now build around 150m² because a lot simply changes during the planning phase. The €300,000 all in all will really never be enough for you. You definitely need a Plan B, or you should speak again with your financing advisor about what financing amount is actually possible. Are you perhaps very conservatively minded or overlooking certain possibilities?