I wish I would've waited. I'm a prime example of your argument. Now i'm 23, with two little boys, and going through my 2nd troubled relationship. I attribute my 'attachment disorder' (as I like to call it) to issues I dealt with growing up. Now that i've made my mistakes, i'm in the process of learning from them, and am playing the cards that god has dealt me. However, I in no way would give my boys up for anything, nor would I have changed anything that i've been through. It's made me a stronger person, especially if and when I get past this bump.
In some cases it works, but in most cases 20 year olds don't know themselves completely yet, so how are they to share themselves with a husband/wife? I know I couldn't, and I wasn't mature enough to make it work. I just ran away. Now, i've landed myself in another situation, and I don't want to run, when in all reality I need to.
Everything happens for a reason though, I suppose.