From semi-personal (family) experience, almost ALL marriages that start at 19, 20, 21, etc end up being less happy than much older couples marrying at age ~35.
Although it might seem a little late, you want to be single for a while! Not that you get trapped in marriage, but if you marry so young it's kind-of inevitable that you'll want to be single again, just to be single. Get all the single shit out of your system and then marry!
Though there are always exceptions, I know plenty of people who married right out of college and are happily married with kids 25 years later.
Another thing- at younger ages physical attraction is the #1 draw to most relationships and the older you get it just becomes about how much you like the person - makes sense that couples who met older and didn't just focus by looks by being picked up at a bar actually LIKE eachother for who they are and live much happier lives due to the fact that they enjoy the social company of their partner