This is something i've been thinking about a bit lately. When i was younger, before i'd lost my virginity, i was still like most red blooded males incredibly horny 99% of the time, i used to
masturbatepanties, bra's and
tights of my aunt/older cousin when i went over their place. I obviously didn't find them sexually attractive but it was my only sexual reference at the time. I also remember when i worked in a supermarket when i was 15, one of the cashiers (a very sexy lady in her 30's who i used to chat to) had to take off her
tights and put them in the bin in the shared toilets because they were ladderer. Well she told me, and i went straight up there afterwards and wore them under my trousers with a raging boner in all day. I used to be concerned that perhaps i had cross-dressing tendancies, and even questioned my sexuality (naively). But it was 'just a phase' i'm now a happily married man in his 30's with a beautiful wife, and no in-case you were wondering i've never tried her underwear on and have no desire too. I look back and laugh. I'm sure you (and he) will do exactly the same. On the other hand if he continues to enjoy wearing ladies underwear, its a prettty harmless pastime, its only clothing, and he's hurting no-one. Hope this helps.
james x