Do only girls and women donate their hair?

That's just not true. I know two men who've been growing and donating their hair to Locks of Love for decades, aging hippies both of them. 

My son grew his hair almost to his waist and donated the hair to Locks of Love for kids with cancer.  Two times. 

He's in the process of growing it out again.

Men also donated when long hair was in. Now not so much, since hair is now short on men.

No. Anyone with hair at least 9 inches long can donate it. My oldest son donated 20 inches when he had his hair cut. He had grown it all through high school and university. 

no, guys can, but not usually, grow out their hair and donate it as well !

No, men do it too.