The oldest pekin ( purebred and weighed just under 12 pounds at its heaviest) I ever had was 6 years old- still alive it was rehomed when I moved interstate- so I dont know how much longer it survived - but I have never encountered leg issues in any of mine. I currently have a pair of utility strain pekins who are about to turn 4 years old. Crumpet is a great layer and has gone broody often. I also have an Aylesbury- who is even heavier than a jumbo Pekin- and no leg problems either- so again... this is why the breeding behind the individual duck and bloodline is more important than the actual breed itself at times. Pekins are a lovely duck for so many reasons, they are also the most common, maybe a reason why it is so common to hear of problems with them- but all ducks breeds have good and bad points- just like dogs cats and many other animals as well.
There are many different strains of Pekin. Here in Australia - most sold are basically just a white duck ( I say this because to improve bloodlines they have been crossed with others breeds many times over generations to improve lines when they become inbred ) - but when compared to the official standards of the breed are nothing like what the pure bred Pekins are. If you really want a jumbo - do some research first into the breeding and strains from where you wish to purchase from. Find out if it really is the right breed for your needs. What qualities do the jumbo have that you like? Is there another breed that might suit just as well?? I would say this for anyone looking at a new breed of duck- not just for those wanting Jumbos. There are so many different breeds - that as long as you know the issues they may have- their good and bad qualities before you make your purchase - at least you know what you can expect and can make an informed decision. Gofasterstripe on here has a jumbo Pekin- I hope she sees this thread and can chime in with her experience with a jumbo.