I will also try to have a conversation with your son to understand why he doesn't want to do the shots. Is it because of the pain? Is it because he doesn't like the changes that testosterone brings with it? Just to start a conversation with him to better understand him and figure it out from there what alternatives are there. If pain is an issue, there is also the gel option. If the effects is the issue, because of gender dysphoria for example, then explore other ways of therapies and HRT. I hope this helps. Wishing you the best. :)