Is it normal to like a guy whose 15 years older than me?

Of course there's nothing wrong with you we like or love whoever pushes the buttons there's no golden rule.
Him a pedo , bs , 15 yrs isn't that much and your old enough , people are just stupid , better get use to that one and just take it for granted. If it was some other situation they'd just find something else to say - that's what people especially friends do.
Don't go marrying him though coz we just don't know ourselves well enough at your age to make that sort of decision especially if his been round the block but you haven't yet.