Why do so many people post these questions like life ends after 30?

I'm 29M, married, living in a large city.

I understand that in my 30's my body will change physically as I age and that eventually I'll start to lose some steam. But like, I in no way think that just because I am in my 30's it means I can no longer do things I enjoy or go out with friends. I don't believe it means there is no more time for "adventures" or fun. Sure, once my wife and I have kids things will change but I still refuse to live by a philosophy now life is just done.

So the question is, why do we all just fall in line with this toxic mindset that life loses all momentum at 30?