Another wheezy person here!
Asthma has unfortunately played a pretty big part in my life. I've had it since i was 5 or 6 but it has got easier over time (apart from a bad chest infection a few years ago which knocked me for months) so that now i only have mild asthma, which is mainly exercise induced. Cold air makes things much worse but thankfully hayfever isn't too much of a problem anymore.
As others have said, to combat it I take my salbutamol 15 mins before exercise and take it easy - listen to your lungs they will let you know when they've had enough!
Allergies can also play a big part - house/dust mites, mould spores, animal fur, foods etc. I can't go anywhere near rabbits - horrible furry little buggers!
My mother also suffers with it as does my youngest son. He's only 3 but we've been in hospital many times with him (including last Xmas, which was nice). He's taking Pulmicort and Salbutamol, and fingers crossed, is getting stronger (loves his bike by the way).
Don't let it take over your life, it can improve immensely through medication, exercise and management. But take it seriously. My cousin didn't. She was only 24 when she died.
On a lighter note I'm hoping to do the Lon Las Cymru next year for the charity Asthma UK. Them hills should test my lungs