Question 573560
This is a trick question. If Billy was 14, and he aged x number of years, then his father would have aged x number of years too. If billy was 21, and his father was 42, and billy aged one year, than his father would age one year, unless he was cryogenically frozen or on another planet further from the sun, in which case his birthdays would just be farther apart. 

The answer is: NO SOLUTION