I'd like to nominate our Better Leisure centres. Their website and leaflets etc always show older people in the marketing. And they do discounts for over 60s. I've always felt the major corporate gyms like Fitness First and Virgin are only for hot young bods (not like mine!) so I feel far more comfortable somewhere like this. They seem a really family friendly gym with loads of facilities for both families and older people.
I've got another 'keen'... Ouch!