I'm 55 years old and noticed a lump in my scrotum after being hit in the groin during pick-up game of baseball? Could this be testicular cancer or am I too old for that?

Could be. Should be checked by a urologist & by ultrasound. Good luck.
Unlikely. No age is too old for testicular cancer. It is probably just related to the accident and unlikely to be cancer. However, if it doesn't go away in a few days, i would suggest an ultrasound.