The older you get the more acceptable it becomes. This isn't a double standard, this is about physiological and psychological maturity of the brain. At 17 you may have all your womanly parts but you are far from a full fledged adult. You are still developing in certain areas of higher order thinking, most importantly logical and rationalized thinking. As easily told by many a college kid, these don't seem to finish until well into the upper 20's if then. :D Also, experiences in your life are significantly different and limited compared to his. Myself, at 17 I knew very little of the world that's out there. Especially sexuality and dangerous manipulative people (not saying this guy is one). Tread carefully, but in any real sense I'd look for someone at your school and less towards someone old enough to be ready to start a family.
All this being said, my earlier point is and continues that as you age, it is more acceptable. My grandparents were 10 years apart. However, they met after my grandmother finished college (24yo and 34yo). Likewise my girlfriends parents are 13 years apart but met when her mom was 23yo.
Best of luck.