Five or six. They've discovered it at the same time as my allergies. We were visiting West Germany and the friends' place we were staying at had cats in every room. My parents saw I wasn't feeling well so they put me in a smoke-free bedroom (eighties, eh) and when it just kept getting worse they finally decided to take me outside for some fresh air. They had tests performed on me not long after. Inhale/exhale curve + exercise, allergy pokeys and the works, to get the definite diagnosis.