Um, pretty much the dream you're living when you're in your 40s, only without kids and a little slower and with more recovery time between events?
When you're FI with kids you're still on a parenting schedule-- either the school (or your homeschool) or your family time. Nights & weekends still tend to be family instead of downtown, although you can certainly enjoy whatever free time you get while they're at school. But it's probably best to be home in the kitchen (perhaps baking cookies) by 3 PM.
I was surprised at how the parenting load ramped up a little during high school. It was more mental & psychological than physical, and teens can get in a lot more trouble a lot more quickly. Teen independence (done right) means that they can make more mistakes which leads to more parenting teachable moments. And, of course, travel with a teen (especially in Hawaii) may be focused on college sports/STEM camps and campus visits. Either that or you stay near home one summer while they're working on driver's ed for their license.
Even in college we tended to plan our travel around the families weekend and the holiday breaks. Once she graduated, though, we started empty-nester slow travel. You roam randomly outside of the peak seasons, find the bargains, and can live like a local instead of the resort lifestyle. Since she's in the Navy ("see the world") we made a couple trips to her Spain homeport. We followed that up with visiting her in Charleston and Norfolk, and we hope to enjoy more of our former homeports with her future duty stations. If the Navy doesn't send her to Asia or Australia then we'll take care of those trips on our own-- not just 2-3 weeks but several months.
My 40s and early 50s felt about the same as my 20s and 30s. However around your mid-50s your body starts to lose its recovery & repair capacity so you become more injury-prone. This is especially frustrating after the second hour when you inadvertently exceed a new limit you didn't know you had. It takes longer to recover and eventually degrades into a full rest day in between sessions. My full-contact taekwondo sparring with weekend clinics & tournaments slowed down to just the regular classes, and then only two nights a week without sparring, and then I stopped training for higher belt levels, and then I just did forms. A couple years ago (at age 55) I had to give away my uniforms & gear before I really hurt myself.
I'm no longer interested in surfing 20-foot waves (or at least not in paying the price for mistakes), and I can see that in 10-20 years I might feel the same way about anything over 10 feet.
Once you finish the first decade of FIRE, your investments are much less susceptible to sequence-of-returns risk and the 80% success rate really starts to take off. You've also optimized your life and your non-discretionary expenses are declining. Lifestyle expansion might kick in a bit... probably not Cessnas or yachts but perhaps nicer hotel rooms or first-class tickets.
I can understand starting the sixth business. Some occupations have no reason to stop working, like doctors, lawyers, journalists, or professors. You might not play a sport anymore but you could referee or coach. I'll keep writing as long as I can string a couple sentences together. The big difference among all of them is that you become more mindful of your time and you're no longer willing to put up with long/late hours or deadlines.
I'll report back with more data in late 2020 when I reach my 60s...
Last year we did a cruise on a smaller ship (the Azamara Journey) with only ~650 passengers. You didn't have to worry about crowds for popular activities and the ship got into the smaller ports, which is very nice, but it's also a slightly livelier ride. Be ready to deal with motion sickness until you get used to the new environment. You will adapt, but it might take a few days.
If you're talking about open-ocean sailing then it's better to take a few overnight trips (or day-sailing in heavy weather) before you sign up for an ocean crossing. Again you'll adapt, but that happens faster when you have the experience to know what to expect.