FWIW I think you nailed it exactly! Older and bigger boats are asking surprisingly low prices and seem to not be able to be given away (probably because the cost of maintenance and upkeep is astronomical). But relatively new boats are always in demand (excepting recessions or other dire financial conditions).
Everyone seems to want the proverbial 'few year old' boat in pristine condition. Unfortunately, the 2008-2009 financial crisis put a lot of boat builders out of business, and the ones that were left built fewer boats than before. Add in the effects of multiple hurricanes down south taking thousands of boats out of existence and it seems to have been a double-whammy of decreased supply with increased demand.
As others have wisely said, a boat is not a rational decision. If you want a boat and can afford one, buy it when you can find one that fits your needs and budget. Being in the situation of having limited remaining time, take it from me - heed the wisdom often offered: time is the most precious resource of all, because no matter what you do or how much money you have, you can never get more of it.
Another piece of wisdom, at the end of life, few people regret the things they did, but much more so regret the things they didn't do.
If you truly want a boat, do it. Don't try to second guess the 'market' and try to time buying at a low. The only way to know when a low point has occurred in any market is when you're looking back at it from a higher point (and conversely, the only way to know when a peak has happened is when you're looking back up at it from a valley). If you're ready to go boating, just go.