I'm thinking that there's something else, other than age, wrong. Gelcoat
, even at 20 & 30 yrs. old, below decks, will be really shiny, and not exhibit the cracks shown in the picture posted.
I think you would be well served by drilling a little hole down into the gelcoat. If there's a cored deck
underneath it -- of any kind -- moisture has got in, and the gelcoat's been flexing. Gelcoat, being really brittle, those would be stress cracks of some kind, most likely. What drilling the hole down is about it to get to a little bit of the core
, and find out if it is dusty dry -- in which case I am joyfully wrong-- or damp, confirming water
If it is dry, fill the hole with epoxy
, and carry out a cosmetic repair
; if not, then you have something structural to consider.
If you can do a cosmetic repair
, then paint
is one option. Most of it is not forever, though, and vulnerable to being chipped and scratched.