I have played 4 teens across 2 households since getting HSY and only one has gotten the puberty milestone. It was the youngest one and he got it within a few sim days of aging to teen. I play on long life and my oldest teen is 3 days away from aging to young adult and hasn't gotten it. I do sometimes get an embarrassed moodlet about acne on teens including those without puberty milestone. I try to use facial cleaner daily but sometimes forget and then it comes up.
ETA. I got Growing Together pack prior to getting HSY pack. I had 4 other teens with Gro pack but prior to HSY and no puberty. I am not sure if you need both packs to get puberty milestone. I have both packs in my original reply about only getting the milestone in 1 of 4 teens.
