As far as I know, boys need to regularly ejaculate for health reasons. We usually achieve that by masturbating, which obviously isn't possible when you're locked in chastity.
In my case, my parents locked me when I was 15. Back then, I knew nothing about prostate and milking and even if I did, my parents would never let me have a dildo. Luckily, I was allowed once a month, so it wasn't a big concern for me.
I wanted to ask other guys here who were also locked as teenagers - how did you manage to do it? If you were also allowed once in a while, how often was it?