As you didn't mention here the desired Medical exam name. To apply for the exams your minimum age should be 17 years.

NEET Age Limit- You must be born on or before January 1, 2002.

AIIMS Age limit-  You should have attained or will attain the age of 17 years as on the December 31 of the year of admission (2018). Born on or after January 2, 2002, are not eligible to apply.

You can check the further information with the given below links.

NEET Eligibility 2018

AIIMS Eligibility 2018

Good Luck!