The label "senior" can vary depending on who you consult
but 7 is pretty average. As for aging, do you mean when most expect a cat to start to look it's age (lol....I have a couple of rambunctious 11 y.o. who would defy any description of "senior"!) that would vary cat per cat
My oldest are 17 (this month) and 16 (as of next month), and this is an age where they begin to look a bit frail.
I've always understood 8 to be a senior but it does depend on the cat I guess. My 18 years olds coat is starting to look what I would call 'starry' - thinning out and seperating rather than looking sleek.
Our vet recommends senior checkups starting at about 8 years old.
Individual appearance of aging & age-related problems seem to vary widely in cats I've had.
My rainbow bridge tortie girl started having health issues at 11, and lived to be 17. She started slowing down & beginning to look frail at 13 or so. Our 16-year-old tuxedo girl is only now beginning to slow down just a little bit, though she's still quite playful and has a gorgeous, plush coat. We started noticing a slight change in her eyes when she was about 10- they get sort of a 'milky' look to them in certain lights. Our other two 10-year-olds act & look almost like they did at 5 - same with our 8-year-old cat.
Good preventive care & regular senior checkups can catch problems early & really make a difference.
Sash is 11 and his annual bloodwork was excellent in Sept. Thank god so far no changes, although I know things can change quickly as they age. Sash still acts pretty much the same and looks no different than when he was 5. He does sleep more though, but still has the nighttime crazies! Lisa & Sash
One thing I'd say about a geriatric cat that looks "frail" or is thinning - I'd have a wellness visit, including bloodwork.
Geriatric cats should have a full blood panel done twice a year, and even that won't necessarily catch problems. Sometimes it seems that they develop overnight.
My Cleo began to have problems at 14, which went undiagnosed despite numerous vet visits til age 15 - and she had to be put to sleep at 16.
Puss was diagnosed with renal disease at 16. Despite the fact that we were already dealing with it with Cleo, I still missed the signs. But I took her in for a geriatric panel and it was found then.
I've been lucky so far, it's almost 4 years later and she's still with me.
My long-winded point being that if a cat is losing weight and looking frail, and it's elderly, there's a good chance there's a reason for it (altho sometimes nothing can be discovered).