If you are 19 now then you must be between 21 or 22 after the completion of your graduation. There is no restrictions in number of attempts you give in CDS exam however age is. A candidate can give the CDS exam in ages ranging from 19 to 25 for different branches.

For IMA, your age should be between 19-24 years. For NA, your age should be between 19-22 years. For AFA your age should be between 19-23 years. For OTA, your age should be between 19-25 years.

The CDS exam helds twice a year so you may give 6-9 attempts after completion of your graduation.