Rolf,
Good topic. My own experience should serve as a caution. I am 49.9 years old and built my first boat at age 14. I have been symptom free up until my current 4 year trimaran building program. In the last year I have severe skin problems with my hands I can only assume is epoxy allergy. I'm two week away from launching but my excitement is tempered by the fact I may never be able to build another high performance boat.
I'm no expert but I noticed some things:
1. Exposure is cumulative - if you are young, better to start with good habits.
2. What seems to matter is your total body exposure - hands, lungs, mouth.
3. Cured epoxy in the "green" state can still be highly irritating.
4. Some epoxies are definately less irritating but once you develop a full blown allergy that dosen't matter. The idea of the smaller the hardner ratio the more irritating is a good rule of thumb.
5. If you want to know if you have an allergy, dilute a very small amount of resin with acetone, swab it on a bandaid with a q-tip, put the bandaid on the inner side of your arm for 48 hours. You will get a reaction if allergic.