Interesting! I`m lucky, I have a wife that loves gardening so I don`t do much 'hands on'.
Something that minimises the need to bend, or to work on one's knees, springs to mind. Younger folks can`t relate to how the body loses flexibility and gets more aches and pains with age. Knees were never designed for kneeling, knee pads help but we only start using them when it's too late.
Maybe consider tools that provide more leverage for cutting/pruning? Strength falls with age and whilst most men are still OK the ladies may struggle more, Mrs W has mild arthritis in her hands and finds the gardening harder even though she still enjoys it. Bigger handles that are easier to grip, or softer grips?
Tools that are height-adjustable? Back problems affect the oldies more and the optimum working height seems more critical, even pushing a lawn more can cause problems if the height isn`t correct.
Perhaps make a list of the physical issues that get worse with age, then consider the popular tools and activities, and try to marry the two together? Food for thought.