As others have said, get a full check up for your own peace of mind.
No age is too young to have problems, my first heart problems started at 16 and had surgery at the same age. Had been given the all clear and just last year I had a small heart attack at the ripe old age of 21 - totally unexpected, no prior symptoms.
Curiously, it is common to have what is thought to be cardiac type pain, but can in fact be esophageal spasming and this can be common under intense exercise according to a few reputable medical journals (just been doing cardiac at uni the last few weeks :p), all the involuntary muscles are innervated by branches of the same nerve so messages can get a bit mixed.
ANYWAY - see your GP for a checkup and they can refer you for further testing if necessary given they'll know your full history better than any of us can! ;)
Seano

