As the gel coat (meaning the very top glossy coating) is already almost 30 years old, and, for some reason, the PO painted over it, I wouldn't be all that concerned about saving what's there.
Hopefully the paint
is latex and will respond to a heat gun and a plastic scraper, Most latex strippers don't bother fiberglass at all so, after testing in a hidden area, you might also use that to soften the paint for removal.
Depending on what you find, the next step(s) may 4-6 coats of ZEPP Wet Look Floor Wax or a lesson on applying Briteside Marine paint via the roll and tip method.
You might take it around first and get several opinions on what's on there before starting to remove it though.
If it turns out that is is brushed on enamel, such as Rust-oleum, all I can say is Good Luck with that.....