Can I add a 15yo as a child under family sharing?

I deleted my 15yo from the family sharing since it seemed to be the only way I could get the find my iPhone to turn off on his phone - since it needed to be replaced. When I tried to add him back- it wants him to be an adult since he is over 13. The select the birthdate autocorrects to 2009 and won’t let me pick an earlier birthdate- is there a way around this that someone can tell me?

Thanks