I think you should let this one go. If your friend's dad won't budge and your friend won't go against his wishes at 21 years of age then for the moment that is just how it is.
The only way this works with the dad never changing his stance is if your friend COMES TO YOU and says he wants to go and doesn't care what dad thinks. Any prodding or helping him come to that point WILL come back to you when it hits the fan. Trust me on this one.
Just as you do what you want and feel comfortable doing you should also let your friend be completely free to do so without any nudging whatsoever. The world is full of fun things to do without HAVING to do your favorite with a bud that isn't completely comfortable with the whole situation.
The only way this works with the dad never changing his stance is if your friend COMES TO YOU and says he wants to go and doesn't care what dad thinks. Any prodding or helping him come to that point WILL come back to you when it hits the fan. Trust me on this one.
Just as you do what you want and feel comfortable doing you should also let your friend be completely free to do so without any nudging whatsoever. The world is full of fun things to do without HAVING to do your favorite with a bud that isn't completely comfortable with the whole situation.