Only girls are to be check if fertile.. Unlike guys.. They can get a girl pregnant any time as long as the girl is fertile.. A girl is fertile when she is ovulating.. And it may differ from one girl to another..
How Do U Know If A Guy Is Not Fertile?
You don't. The ONLY way a guy does not produce sperm is if the testicles are gone. Don't believe anything else. All it takes is 1 sperm out of thousands. USE PROTECTION.