Is this an old wives tale, my grandma told me ?

Nope it is not even an old wives tale. In order to be an old wive's tale it would have to be something that at some point somebody other than your grandma believed. all it is, It is just something your grandmother made up, and though she may be an old wife it is just her opinion, not an actual old wives tale

Masturbation IS solo sex-- it is the same physiological act for a male whether he uses his hand or a willing and available vagina. the end result- climax and ejaculation are the same. So grandmother is correct. The old wives tales are all the myths associated with masturbation. Since it IS sex, the myths like growing hair and other stuff are just stupid myths since the same thing would happen with vaginal sex.

Old wives tale

Many men seek sexual intercourse just for physical gratification, yes.

That doesn't mean that partnered intimacy cannot be for the enjoyment of both partners.

When you are of appropriate age [IDK how old you are now] and get married, you will have sex with your spouse in a loving and deeply meaningful way that brings joy to you both.

well its true sometimes but sometimes its also to pleasure hismate and to because sometimes they want kids