Her mom is just protecting her daughter and doesn't want her to get pregnant at a young age.  I know you say you're not in it for her body, but you're still young and if you two were alone, making out, those hormones are going to start kicking in and soon enough you're going to be in a situation where you don't have any condoms on you, and the next thing you know is your penis is stuck in her vagina without a condom (not trying to be funny).  You're at that age where your hormones basically control almost everything you do.  Also, if I was a mother (I'm a girl By the way) and had a daughter I wouldn't want her dating someone two years older than her either (in fact, I wouldn't want her dating period.)  Even so, if you ever get in that situation where you are alone with her, have some condoms on you, but remember condoms break, and you can possibly get one past the pill.  I'm not saying you want to have sex with her, I'm just saying spoon happens when or if you're alone with someone you like.