Wow there is a lot of ignorance in these "answers". First of all, if you're 13, you are in no way qualified to give advice in this matter. On what life experience are you drawing for this "advice"? That's right, none.
So he's almost 5 years older... No big deal if she's 30 and he's 35. However at this point, he could be arrested for doing the things they're going to want to do.
Here's some rules of thumb:
No "dating" until 7th grade.
"dating" at this point consists of spending supervised time together outside of school, nothing more, and only within the same grade.
Once in high school, dating allowed within 1 year of grade.
And for you little misfits saying "mom has no right to say anything because she had me at 15", you're simply too ignorant to describe. Do you think it was easy for your mother to be a mother at 15? She's trying to save you the hard times and emotional damage that comes along with becoming a parent at that age. At 15, you're not capable of properly caring for yourself, let alone a child.