Anytime just wait for it. Have him hold your stomach where baby has been moving. Baby just has to get strong enough get the outsiders to feel : P when I started drinking the boost protein shakes I swear she was super women right after. :)
My bf couldn't feel the kick til around 27wks BUT he was able to see his kicks before then! So I'm sure anytime soon!
All women will at different points. Average is anywhere from 20-27 weeks, but usually around 20-25. My husband was able to see and fetal kicks with my daughter at 20 weeks or do.