Is this old age or something more serious?

[SomethingProfound]

My cat is about 14 (a rescue cat so can't be 100%).

Recently she has started grooming one spot on her back excessively and has one spot that seems to of gone totally balled (between her shoulder blades), is eating less and looks rather thin, and her once black coat is going brown she also has become a lot more affectionate which is very unusual for her.

I have taken her to the vet and her blood test came back normal, has anyone else experienced this is it worth getting as second opinion or is she just old?

Excessive grooming and the bald spot could be the allergy to fleas that some cats have. However:
My older cat has a baldish patch between his shoulder blades too though and is treated with frontline so fleas aren't a problem. I have wondered if he gets bitten there by other cats. He is/was an agressive neutered tom.
He has also developed unusual [for him] habits such as staying in a lot and preferring wet food to dry. Older cats are worrying aren't they.