Persons with Benchmark Disabilities (PwD) get age relaxation over and above the normal age limit in most central government recruitments.
The relaxation is generally 10 years for PwD candidates, and it increases further when combined with SC/ST or OBC reservation as per government rules.
You need a valid disability certificate in the prescribed format from a competent medical authority.
The exact relaxation and eligibility conditions are given in each recruitment notification, so always read that document before applying.