Just so you "know before you go", the central part of the Tower of London - the White Tower - was built around 950 years ago by William the Conqueror. Obviously there have been additions and repairs since then, but saying it was rebuilt in 1962 sounds like the Beefeater was having a bit of fun
There are plenty of UK companies offering organized tours and, with the utility of the internet and your credit card, you would be well-advised to use one of them, rather than a travel agent local to The Villages.
The cost of tours will vary enormously depending on the quality of the accommodation used, so your choice of company will be dictated to some extent by your budget.
England may be small compared to the USA but there is a lot to see, and seven days to do the lot would be exhausting and barely scratch the surface. I would advise choosing a smaller area to cover and enjoy a more relaxed in-depth trip.