Dear Irfana, if you are talking about KEAM, to fulfill the eligibility criteria for KEAM 2019,  a candidate should be of minimum of 17 years of age as on December 31, 2019. There is no upper age limit.Candidates seeking admission in engineering courses must have passed 12th or equivalent exam from any recognized board. So there is no set no. of attempts to appear for KEAM as long as you fulfil the age and education criteria.