*shrugs* Age is no matter really. It comes down to how mature the person is. I'm 23, my fiance is 19, we are getting married in October and we also met online. I would not make this decision lightly if I didn't feel she was ready and shes mature enough to know she is and her parents obviousely agree cause they are happy and helping us.
As far as the online thing, I've done it a few times. While it's a great way to learn about someone, a few things to keep in mind. While you can learn some things about a person from them talking on a computer, you can't learn everything. More often than not, a person isn't going to tell you about all the bad things. Another thing is how long are you planning to keep it online before you two decide that one or the other has to move to be closer. Living apart from the person you love is hell and difficult to keep together. Get to know the friends and family of the person. DON'T BE SECRETIVE ABOUT IT. If they won't involve you in their life with friends/family, it's not a healthy relationship and will continue not to be till you do...