Why’s that? People grow a lot with maturity and knowing what they actually want out of life between 25-40.
Of course this process never really stops but between those ages you’re going through a lot of transitions and new experiences. You’re still doing a lot growing up during that period.
It’s not unfair to say that marrying young is a bad idea because you don’t really know who you are yet and there is a lot of opportunity to grow away from your spouse.
By the time you’re much older a lot of this is out of the way. You’re lot further into your career and in a more stable place.
Anyway just my experiences but I don’t think marrying young is a great idea. I’m in my late 30s and I feel like a completely different person compared to my early 20s.