I could go on at length about the pitfalls and traps in being involved with younger women...so I will! 🙂
I'll be the last person to tell you not to get involved with younger chicks...but you need to keep it in perspective. I would NOT expect anything long-term or too terribly deep to come of it. "Dating" is one thing, a "relationship" is quite another. Lemme fill you in on something about 19 year old girls (and guys for that matter, so no offense to the ladies of that age group here)...they're flighty and easily distracted by shiny objects. You said this girl is "crushing" on you. That's exactly it...she's crushing, not feeling anything that could lead to love.
Now, this could be fun for awhile, and if that's all you're concerned about, go for it! This has nothing to do with morality, that's socially-imposed. There are just a few things that guys our age need to look out for when involved with MUCH younger girls. Again, this is nothing against anyone in particular, just the things that often creep up in these dynamics.
* You will have little in common socially.
* Her life will chug along at a much faster pace than you are going to want to keep up with after a certain amount of time.
* If it does last awhile, you're gonna want to hope her parents are the rare breed that are gonna be cool with it. Not that you'll be dealing with any particular threat, per se, but expect a load of discomfort for both of you. And that's not even mentioning her friends who WILL know EVERYTHING the moment it happens whether you're aware of it or not.
* Young women often "crush" and then become overwhelmed if the object of their fantasy actually takes them up on it. Like a dog finally catching that car he's chasing...now what?
* SOME (not all, but more than you'd think) young women can become very manipulative when involved with an older man they feel has "won" something..."gotten the hot young chick" sorta thing. If they intend to or not, it's often natural for an emotionally and socially underdeveloped girl (ie: most women under 27 or so) to use her sexuality. And, it's often in the nature of the older man to fall for it. Just the way the species is.
Of course, men play their part in the issues with these dynamics. I know men who just cannot relate to women their own age, can't be equal partners, have some sort of dominance-confusion issues or whatever...and just string along a series of young girls 'cuz that's all they can emotionally handle.
This may sound very disparaging, but it's basically just to help you put some things into perspective. Of course, there are always exceptions. I know of a two very successful couples (vanilla, even, so it's not a kink bond)...in one, the guy's 42 and the woman is 28, another with a 51 year old man and a 27 year old woman. Now, 19? Probably not gonna work long-term.
If this is a kink thing, like, she's into your fetish, just take it as that and have fun, expect little else. Ever notice that most of the successful kink video producers (and I'm talking the real ones, not just the morons with cameras) use 19 year old models/subs...but are married to women around their own age? Hell, even Shy and I, a couple who like to play with others, have a lower age-limit when it comes to who we'll play with. It's a maturity thing, and we're just talking about play here.
If you are going to pursue this, find out a bit about her, see what she's like outside of anything sexual, and put the whole thing in perspective. That's my advice. 😉