I found 6/20, but there seem to be more then 1 date. plz help me

i think at the begining of each season when teams get new youngsters

usually 19th June for English leagues... for the premiership anyway!

I also found new regens b/w july to august and somewhere near december.

it all depends on the leagues you have active, as a lot of them have different start dates. the scandinavian leagues tend to get regens in around february time, and i think some of the eastern european ones are in january...