This is Queen Maple on her 4th birthday (over a decade ago). I still think of her as this because, well, she hasn't changed a whole lot personality-wise or anything else. However, a year and a half ago, her blood work showed she was in early stage chronic kidney disease (CKD). This was by no means my first CKD rodeo, but there are some things that I have forgotten, despite knowing that this was how I realized Lucky (the tux boy all over anything to do with this business) was sick.
Maple has anxiety issues as well, and is on Prozac as she was urinating inappropriately, so when she started getting more grumpy than usual last year, I took it as part of her anxiety. I saw spots on the carpet that I thought were pee (as she occasionally voided her bladder when really upset). Then in recent weeks, she was throwing up occasionally, but not enough to trip my radar. Then, last weekend, I witnessed her throwing up a waterfall of bile. Now, as previously stated, I've been down the CKD road, so I'd been giving Pepcid to her on occasion (note: please always contact your vet before administering a new medication for the first time!). After the waterfall of bile incident, I realized it was probably time to start doing Pepcid on a daily basis. I'm happy to say that not only is she doing better, no more throwing up, but also no more pee spots here and there (which I'm thinking may actually have been bile - I felt so bad when I thought that). And, she seems in a much better mood!
To the point of this post - grumpiness isn't always just a sign that your cat is getting older. It is VERY often a side effect of physical symptoms. Think about it, when you don't feel well, you may not react very well to things or people in your environment either!
With Maple, since she's had a history of being moody and having anxiety, it was very hard to tell that it was tied to a physical issue, and took other issues (throwing up) for me to realize it. If you have a geriatric cat though, please don't ignore this symptom, or write it off as old age. Changes in mood can be, and often are, indicators of physical problems. With Lucky, it was very obvious because he never ever growled at me until he got sick. Of course, this is an indicator that Maple's kidney disease is progressing. Thankfully, she is normal otherwise. Still eating up a storm. I have learned to pay a lot more attention to her pattern of moodiness though so that I can determine what is normal, vs what is not.