@cmerry, there is a lot of stuff here, some of which I'm probably not the best person to comment on anyway.
firstly, your correct that adult relationships don't bother about age gaps, my lady is 9 years older than I am, however, the younger one party is, the more the age gap matters.
think of it this way, a five year old and 8 year old kid are in almost different worlds. a 10 and 13 year old might be friends, but there will always be a clear big brother/big sister, where as someone who is 19 and someone who is 22 are far more on an equal footing.
16 is still at the younger age in relationship terms, especially since there is so much paranoia these days about child abuse, ---- admittedly less when younger party is male, but it's still there.
So, there is a lot of complexity for her at the moment, even more if as you said, she saw you when you were twelve and you behaved in a far less mature fashion.
I'll also say from personal experience, you describe this as "You really feeling something" and as "more than a crush", however bare in mind that unless you actually get an indication of what the other person is feeling, then things will always be of the one sided admiration sort, however deep that admiration is, and unless you discuss matters directly, in person, in real time, it's hard to get that via text message only.
I exchanged casual emails with my lady for a good six months and never realised there was chemistry or attraction until we met in person.
Even after that point, we did everything via long distance phone, and it took three months of phone calls as friends.
I'm not denying your feelings for her, what I'm questioning is whether those feelings are one way or indicate an actual connection.
I'm also wondering, you mention "not wanting to seem desperate" however bare in mind women are people too and despite all the "man must ask first" crap, can be equally confused about things, my lady said she had suspicions about the way I felt, but things which to me seemed very blatant, she did not pick up at all, and with all of the business with the age gap etc, it's possible this lady is in an equally confused position and is avoiding the issue, or worse, has found something you said creepy because (as we all know from forum drama), text is not voice, and misunderstandings are possible.
You've done the first thing I'd suggest, just sending a casual message, but depending upon your past history this might or might not result in anything.
if this lady chooses to get back in touch, just chat and be friends for a while (as I've said several times in this topic), then at some point, see if you can have a real time conversation over skype etc, and see what happens.
Lastly, I'm going to say something infuriating. Relax! your sixteen, and everyone at sixteen, women included, has a deep attraction to someone else which doesn't work out.
In my case I was seventeen, and there was far more baggage involved.
You have time, just relax, meet girls casually and treat them as friends, try to associate with girls with brains, don't be a bastard and things will work out eventually.
If they worked out for me, they'll work out for everyone, and most people don't have my hangups.
sorry, I know it's trite, but having lived it, I can say it's actually true.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)