Most people won't care, some will call you a paedophile because they don't know what it means and some will object because a 17 year old should be 100% school work and no romance.
I think this is fine, it doesn’t sound like you’re manipulating her in any way due to her age or anything so i’d say it’s alright. Some people may think you’re weird but in the grand scheme of things, you’re much closer in mental age maturity, unlike someone who 14 (Y9) and 16 (Y11) for example, that’s a lot different.