There is no upper age limit for CLAT.
The NIOS is treated as equivalent examination so it does not prevent you from sitting for the CLAT.
As regards minimum percentage of marks in the qualifying examination (i.e., 10+2 or an equivalent examination), the candidates must have secured:
Forty five percent (45%) marks or its equivalent grade in case of candidates belonging to General / OBC / PWD / NRI / PIO / OCI categories
Forty Percent (40%) marks or equivalent in case of candidates belonging to SC/ST categories.