Older Labrador when is it time ?

My yellow lab Biscuit is approaching the age 14, aside from the lumps (covered with them) he still is eager to walk And beg for food. My question is when did you know it’s time ? Did you do a wellness check ? I’m asking as recently it seems like if we give him anything other the dry kibbles it has created explosive diarrhea, and since he’s 14 he can’t hold anymore and has started having some accidents on the floor, even one time he pooped while sleeping.

Also started getting really heavy pants, even though he doesn’t seem discomfort at all. I’m assuming it’s due to the lumps he has.