Great question.  When I was a teenager with hard luck asthma in the 1980s I asked my doctor the same question, and he had no answer for me.  The good news for you is I have since found the answer.

Asthma experts now believe that for about 90% of asthmatics the life expectance is the same as for those who do not have asthma -- 80 years.  The key, however, is for your parents and doctors or you to recognize right away that you have asthma and to treat it immediately and agressively.  So long as your acute asthma attacks are treated swiftly, you should have no long term problems.

Likewise, once your asthma is diagnosed you must become a gallant asthmatic (click here and here).  You must be educated about your asthma.  You must learn what your asthma triggers are.  You must avoid your asthma triggers to the best of your ability. 

Likewise, you and your doctor must work together to develop an Asthma Action Plan (AAP) that works best for you.  Your asthma AAP will help you decide when to use your rescue inhaler, when to call your doctor, and when to have someone take you to the emergency room (or call an ambulance).

Another key is that you must be aware that asthma has two components:  airway constriction that makes you feel short of breath (this can be treated with your rescue

inhaler)  and chronic inflammation, which is swelling and redness of your air passages (bronchioles) that's always there.  Both of these components of asthma can be treated with PREVENTATIVE medicines like Advair and Symbicort.

So long as you are always compliant with your preventative (controller) asthma meds you should be able to keep your asthma in check, and thus develop no long term complication.

However, goofus asthmatics (click here and here) who do not take their meds as prescribed, and who do not follow an AAP, can develop lung scarring that can complicate the airways and make asthma more difficult to control (however it is still possible). 

Likewise, asthmatics born before this modern wisdom (as myself) may also have developed lung scarring if too many of their asthma attacks went untreated.  This shouldn't happen anymore.  In fact, according this press release, the number of severe asthmatics is going down. 

I hope this is some good information for you.  If you have further questions be sure to let me know.