Not a singer, but owner/driver of 2 teen boys. No reluctance to sing at home, just a tendency to turn wellknown songs into political satires which they would sing at the top of their voices in close harmony, hamming it up...I learned to keep the car windows UP! They don't sing quite so much now that the novelty has worn off.
Noticed two things: 1) one son is not really a confident singer, but a boy with a broken voice is supposed to be immediately able to sing harmony, which often entails reading music confidently and being able to maintain a part against the melody. At the same time, he started listening more to female singers, especially ones with mouse-like high-pitched voices (

Not reading this, I hope...

).
Didn't dislike singing, but very unconfident - I don't know the solution. At home, he sings melody as he has a lighter voice, and the other son harmonizes with him in his lower voice, so he doesn't have to cope with the demands of harmony.
2) other son loves to sing, but definitely noticed a reduced range. We had a lot of scat singing sessions while driving along! I don't know why he found scat so attractive just at that age, but he did.
Plainchant? Recitative?