Cracks in gel coat are stress cracks because the underlying laminate is flexing or was flexed more than the gel coat could follow; or, and way more likely, the gel coat is too thick. Gel coat is a relatively non flexing medium that has a real problem with cracking with flexing of the underlying grp laminate. Spray it on too thick and the gelcoat will crack just by walking over it. The deck on my last boat was laid up on a cold day. They sprayed way too much gelcoat on because it ran off the high side and pooled on the down side of the mold. Had to grind all the gelcoat off the low points of the deck cause it was a nest of gel coat cracks.

Never heard that gel coat is subject to oxidize caused cracking.