I hate it when people say this couple is pedophilia. Just because he's a baby dragon doesn't mean he's still a baby in the literal sense, all things considered. And Rarity doesn't act like she's older than 17 or 18.
Apparently some people are under that impression. I came across comments like that on a couple of stamps about the couple. Maybe if Spike weren't called a "baby dragon", he looked a bit older, and we knew the official ages, people wouldn't make that assumption.