Childhood asthma is not uncommon but often dies away after puberty. The doctors refer to it as pre-pubertal asthma for this reason.
I suffered from pre-pubertal asthma, which I remember as being particularly uncomfortable and incapacitating for several years during my younger life. It did die away, however, and has not stopped me from military and civilian commercial flying as a pilot ever since. My peak flow test has never been strong but I have always declared my childhood condition and the doctors have never been particularly worried.
Post-pubertal asthma is a different matter, though, and the doctors, miltary or civil, will want to be absolutely sure that there is no chance that it may incapacitate you in flight. You will, therefore, be subjected to much more stringent questioning and medical checks to ensure that this does not happen. Even the slightest risk of an incapacitating attack in flight will jeopardize your chances of passing an aircrew medical.
Be very wary of being economical with the truth about your past. You will invariably find nowadays that you have to sign an authorization permitting the relevant doctors to check your GP's records. If they then find you have lied, they will not be sympathetic.