My old guy is 13 years old. He also sleeps more these days and has had some other issues. He doesnt have lumps on his back but has gotten little worts as he has aged. He just has started having issues with his back legs the past few months. Everything before then seemed like usual old age aches. I go by quality of life, or try to as best I can. As long as he wants to eat and wants to go for his walks he seems happy. When the day comes he doesnt want to go for his walks I think I'll know. So idk if yours has any favorite activities or treats you could judge by. They are prone to getting cysts and that's what mine has also had. But I've still gotten them checked by a vet to make sure it's not more. Mostly just so I know how to care for him if it was worse news.