She says "i didn't tell him my age and he didn't ask". Could be she looked older (and seemed more mature) than 15? Some 15 yr old girls I know look at least 18!
I doubt rock stars in that era asked every girl who was 'dressing to impress them' what age they were if they didn't look at all like 15 (after all, not much separates 15 yrs from 16 yrs, the age of consent.)
It was still statutary rape by law, but it can be bit of a minefield for men if their intentions are not bad ones.