Angus is quite a bit older but I didn't start him on Senior till he was about 11. He maintained pretty much the same weight and had a pretty high energy level.
As soon as I started to see him put on weight and slow down that's when I stared him on a senior food (it also has glucosamine and condrotin).
He's never minded the taste of the senior food, but then again he's never been a very picky eater

I personally think it would be a good idea.