Honestly I believe its all about who you are personally and where you are in your life. DH and I got married when we had both graduated college. I was 22 and turned 23 the next month, he was 25 and turned 26 a couple months later. We got married right after some friends of ours and a year or more before most of our peers. We were definently ready... college was all the life experience we needed to get started and we have since kept steady jobs, bought a house, and started to build a business together.
On the flip side, friends who got married after us are now having kids, and we are probably a few more years away from that, emotionally and financially. I was never more ready to get married, but the next step is a little scarier to me for whatever reason.
My sister-in-law on the other hand who is less than year younger than me would like to get married, but is dating someone who at my age (27) has already been married and divorced and really doesn't seem to want that right now, so she is still not married, but then again, most of her friends are not married either.
Now we are 4 years later and I don't think we got married too young at all. We are gaining life experience together and we have luckily been very stable in our married life so far!