I'm an active 61, my wife an active 58. We are not prone to any physical disabilities and would like to think we act "youngish" for our age... so if you're looking for observations by some sour-grapes-cruisers this one may not be for you !
The "Gem" is a much prettier ship than the ghastly photos of it on the internet would have you perceive. It's clean, (fairly) well managed, has a lot of stuff to do for the younger set (rock walls, baby-sitting facilities, etc.), and like most ships has good, and not-so-good qualities.
The good: The music... Selwyn Wright & Taylor (?) are both unique and wonderful piano players, two of the best I've heard, and as a former musician myself you'd best off believe me on my assessment of the two. "Ken", a singing jazz oriented guitarist is top notch, and a female guitarist/vocalist who tends to be more pop orients is also well worth hearing and built-up a substantial fan-base during the voyage. With the exception of the Alto sax player "Dale", the stage band is marginal at best... almost embarrassingly so at times. If you have a critical ear stay away from them.