Hi Aspirant,

You can write Kcet as many times you want between 21 to 24 years.There are no time limit as such and you can give once in a year.To cancel the admission you need to inform the official of the board under which you have taken admission.Moreover your candidature gets automatically cancelled once you remain inactive however its better to reach to the officials of the board through email or helpdesk to reach any conclusion.

Hopw it helps!!