Many disabilities do not preclude flying solo. Each case must be decided on its merits, and safety is the only issue. Anyone who has sound senses and a sound upper body can fly a glider, and control rather than strength is the main requirement.
We have built a Seat Hoist to ease the problems of getting into and out of a glider for wheelchair-bound people or others with restricted movement.
It’s impossible to fly solo if you can’t use the rudder. We have a hand-rudder adaptation for the K21, which allows the rudder to be controlled by a lever at the pilot’s left hand, instead of the rudder pedals.
The K21 is a two-seater trainer that flies reasonably well cross-country, and which can also be flown solo. The rudder control works from the front and back seats, so a disabled pilot can progress to P1 or instructor ratings.