what is the eligibility to hold a atm card?

I am not familiar with the laws in India, but in the U.S. you must be at least 18 years old to have a bank account.

there is no eligibility criteria except the fact that you must be an account holder in the respective bank. I think if your brother is only 15 years of age, he can certainly be a partner in the account if and only if one of your parents or a guardian partners the account but he cannot own an ATM card for sure at such a tender age.

Open a joint account in any bank you want. First name should be of your parent, and the second name should be of your brother. It will basically a minor's account maintained by your parents. The bank will provide an ATM card to both the holders. So, your brother will be able to hold and use the card.

In america most bank as a way to encourage good fiscal spending allow highschools to have an atm/debit card that is cosigned with their parents.

This is good to teach them to balance a check book and manage money.

u should be atleast 18 years old to hold an atm card