SlimmB:
huh

OP, she's 17 years, and you ain't treating her like a 17years old girl rather you treating her like you're inlove with your mate! you sound like you don't know your worth yet, or i say you suffering from a low self-esteem, sorry if i sound rude.
Anyway, there's no problem without solution all you need to do is change your formula before it to late.

Step 1: accept the fact that she's a 17 years old girl and treat her like one, for instance, you don't ask for her permission for anything, but don't give her the impression like it an order, but make it sound like it an authority, you need to impact this into her... very important.

Step 2: She sweet 17, so accept that FACT, i.e she so interested in romance right now and not thinking about the future or consequence. Age 25, you must know how to get under a girl pant sharp sharp, if not then you've lost in women battle!

Step 3: probably the last i'm gonna give. My brother no stress yourself at all for the girl matter, her body dey sweet her because it her nature and she can't control it... spend only when it necessary, don't take her out, invite her over again, and just give her something to take, if she refuses it, frown your face and be like "what's the meaning of that " she'll be shock or want to over react but she'll respect you cause of the age gap, then try all the tricks you've got just to make her feel at home and relax, if it one room apartment you've got,( but if it not, do it on your long chair in the sitting room) make sure she sit on your bed/chair, and try to be fun enough so you could relax your head on her laps if she react then be like "What's it again na wetting be the big deal na don't you see am tire, just let me be like this for at least 2 mins jawee(you must be in that position for more than 10 mins), if you rest your head on her laps and look up, brother i believe you know the way forward

Lol...
She's too young though. Any gal below 19 years (not even 18) is too young IMHO and a no-no for me. The Op should be thinking of dating gals in early twenties 20/21 years old.
But yea...I can say your trick will most likely work. Seems you have got "relevant" experience in the subject matter.