Senior cat food for multiple cats

My mom has 3 cats, two at 5 years and one at 9. She feeds them Premium Edge. She thought about getting the 9 year old onto senior cat food but she free feeds them all. The only difference between the senior and adult food is glucosimine chondroitin (or however you spell it) which is for joint care. Is there any harm in 5 year old cats getting this or should she hold off on switching to senior food for the older cat?

The only things that might factor in are these:
~all cats are in perfect health, never really had any health issues either
~all are a perfectly fine weight, the senior cat being a very small thin cat naturally
~the senior cats coat is dull and almost oily where the others are shiny and smooth
~we are ordering some (crap I can't remember the name) but it is a powder that goes on their food for the senior cat in her wet food or treats. I know a lot of people who swear by it for helping dry and dull coats. I will get back to this with the name, just slipped my mind.

So is switching to senior food for he older cat necessary yet?

No senior food is fine for that age group,....Senior and light foods are "okayed " for all ADULT cats/// KITTENS should never be feed senior

with a coat issue has the 9 yr old had a senior panel

Of the supplement is missing link good luck I have found it not to be terribly effective..

is their a protein and fat difference in the adult vs senior food???

Oh yes! Missing Link! I was going to try it, I know a number of people who thought it worked wonderfully as long as it is consistantly used for a couple months. No immediate results.

So you are saying don't worry about the senior food for awhile yet huh?

The 9 year old has not but she has always been that way since she got her adult coat. My mom bought her when she was like 8 weeks old. I will suggest that to her as something she should probably do soon.

I will check on the protein and fat thing, I don't know and I don't think my mom would have thought to check that.

the only benifit other than jts in senior foods in dry foods is the lower protein and fat which many think aids it preventing or at least putting off the "senior ailments"... I do know it helped with Kandie and her CRF in the beginning..