Our cat is about 14 (former farm cat so we're not entirely sure). Rural outdoor cat all her life and very territorial, so has been in a fair fights over the years and I imagine these have left her with one or two 'twinges'. However, she doesn't seem to be in pain - contrary to what I've been told about other cats, she has always made it very obvious when something is hurting her.
She now mostly stays indoors, has retired from hunting and is more ginger jumping up and down from high places, but is still pretty much the same as she always was. However, when she's trying to wash she's struggling to reach the very lowest part of her back - tends to arrange herself to do it, turn round and round a bit and then give up. She can wash all her other bits, including the traditional leg-hitch.
She's the oldest cat I've ever had so I'm not sure how to deal with older cats getting stiffer. Not the cuddliest but I could maybe have a go at brushing her if she can't manage it herself, although I'm not sure she'd cooperate. Does anyone have recommendations for cat brushes, or other help we could give?