I found my husband's second birth certificate

Quick one, is football age a thing people do outside football? Because I found a second birth certificate for my husband in his mother's wardrobe, brown envelope, under her wrappers. Same name, same hospital. Different year. The one I know says he's 44. This one says 51. So I married a man seven years older than the man I married. His mum walked in on me holding it. She didn't even blink. She said football age, put it back. That's all. She went back to her cooking.