We just sailed the eastern Carribean on the Grand 2 weeks ago. I'd venture to say the average age on our cruise was mid/late-40's. Yes, there were several older folks, but also a lot in the 20's and 30's, and at least a couple hundred kids/teens too. We're in our early 30's, and the couple we travelled with is in their late 30's/early 40's. Our dinner companions were a couple in their late 40's and another in their late 50's.
Really, there was such a mix of ages that it was never a consideration. We certainly never felt out of place, and there is so much going on, such a variety of things to do, age never even enter our minds. Everyone on the ship has something in common too, just by virtue of being there.
I can't speak for the Golden, but nothing I've heard suggests older folks steer towards that ship in particular. Quite frankly, I think we would have enjoyed ourselves just as much even if the crowd was a great deal older. It really just didn't seem to matter.