He didn't say he was gonna have sex with her. In my opinion its fine, my boyf is 5 years older than me, i know that is kinda different cos i'm 19 but, if he is ok with the no sex thing and she is happy to be with an older guy then let them.
Everytime we get a thread like this everyone is all of a sudden hearing alarm bells about sex, not everyone is sex mad, some people actually care about the girls they are with, and are happy to wait until its legal.
If you did do it you wouldn't be done for rape unless she didn't consent and it was actually rape but you would be done for unlawful sex. You would only be done for rape with or wothout consent if she was under the age of 13.