It really will depend on your individual dogs. If they are "old" 11 year olds, it may be difficult. My Digital the brindlewonderkid was a "younger" 11 year old. In fact, his best year competing in agility was as a 10 year old. And when he was 10, I did add a puppy, but at that time I had 10 yr old Digital, 9 year old Jet (the trying) and 4 year old Mucha the malinois, so my puppy had a younger dog ( the mali) to play with to take some attention off the old guys. This actually worked out fine as Digital (but not so much Jet) would play with her, but when he had enough, she still had another dog to play with. Today with Digital at 15.5, Jet at 14.5, Zest! (the "puppy" I added) at 5.5 and Pearl-petual Motion (mali #2) at 5, I would not hesitate to add a puppy (if other things were right) BUT I'd be prepared to run interfearance between new puppy and the old guys. However, my dogs are pretty accepting of other dogs. And my old guys have aged really well and haven't really shown much in the way of arthritis until the last little bit.