Sure hope you enjoy your first FOD meeting. I agree with Ron and Jon, that you most likely will be the youngest there...but you will be welcomed warmly.
My guess is you'll find other young adult gay cruisers on the ship. Most of them don't want to "hang out with us older guys"
The FOD meetings can be relatively small or a huge turn-out. It really depends on the ship and itinerary.
On my last cruise, last September out of Barcelona, there were about 100+ gay men and a large handful of lesbians.
Not all young / older gay men attend the FOD...my sense is your gaydar will help you find others to hang out with and get to know.
In any event, have a great cruise!