I can't confirm the information in the table is correct, because it is wholly based on the information I've collected 'boat watching'. However, it does give a rough guide to the ages of boats, although there are many exceptions, hence the dates in the table should not be taken as definitive.
Originally I assume no boats had registration numbers, and in many cases unpowered craft (e.g. yachts) still don't - the Hunter's fleet is a prime example. However, registration numbers seem to have appeared on craft during the 1930s. These consisted of a letter followed by upto 3 numbers. First 'B' was used for craft from the Bure and its tributaries (Northern Broads), 'Y' for craft from the Yare and its tributaries and 'W' for craft from the Waveney. This system was replaced by a more date-based system in the 1950s. This continued into the late 1980s when the letters were exhausted. Initially some of the older letters were reused (B,N,S,T) making dating more difficult, although a fibreglass 'B' reg boat is not going to be 1930s vintage! In the early 1990s, the order was then reversed, to give 3 numbers followed by a letter. Finally, in 2017 the numbers were changed to 4 digits followed by a letter.