Is it possible to increase height after 21?

Depends on bone age: The potential additional length anyone can expect depends on areas in the long bones (arms, legs, fingers)called growth plates. This is where growth occurs and an active open growth plate means more growth is possible. An xray of the hands & wrists can be evaluated for bone maturity since there are many growth centers to see. If your bone maturity is > 18yo you are done growing taller.