Q. Until when can the father of the bar mitzva boy say the bracha of baruch sheptarani, if he didn’t say it at the bar mitzva?

A. Although, we don’t recite this brocho with the name of Hashem, Poskim (Ketzos Hashulchan 65, Michtam Ledovid 13) maintain that it should be said until thirty days after the bar mitzva.
Horav Shlomo Miller’s opinion is similar.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a