U. S. Coast Guard pfd regulations

[Bean]

And, let's not lose sight of the fact that each state and locality, might impose their own rules which might exceed the CG regs. 

[2Rivers]

And, let's not lose sight of the fact that each state and locality, might impose their own rules which might exceed the CG regs.

Very good point!
http://www.uscgboating.org/regulations/state-boating-laws.php
Click onto 4.9 "Life Jackets" for per state details.
Note: These were issued back in 2008, so things may have changed in some states. Unfortunately I can't find an updated one.

[Bean]

Considering the local air/water temp, this make perfect sense in NY, and not so much in south west Florida:

New York - (must wear a PFD)
 
1. Anyone <12 years of age on a vessel <65 feet, unless situated in an enclosed cabin; 2. Anyone towed behind a vessel; 3. Anyone on a personal watercraft; 4. Anyone on a vessel <21 feet between Nov 1st and May 1st.

In the colder climes, too many die every year falling overboard while standing and taking a leak over the side.