Curate, connect, and discover
Death Noters remember that Near is capable of aging and is currently 27 in canon. He was 12 when first introduced, 17 when he started and 18 by the time the case ended. He was 21 in the C-Kira Story and 27 in A-Kira.
Stop treating him like he's oblivious to sex as well, it's likely they learned about it at some point. Wammy's wasn't a fucking kindergarten where all they did was macaroni art and draw houses.