How old was Alexander Fleming when he discovered penicillin?

Fleming did not invent penicillin, he discovered it by accident when it ruined an experiment he was doing trying to culture bacteria. It took many others and the expediency of wartime emergency funding to invent the technologies needed to mass produce penicillin as a drug.

Many later antibiotics related to penicillin were later invented in labs, but penicillin is not anyone's invention as it is a natural substance made by a type of fungus.