I see there are age categories for the record on http://www.beermile.com/records, with the over 50s in the Grand Masters. Surely we have some world class talent in that age group. What odds would you give on Ovett vs Cram vs Coe?
This is surely an event when our heritage of cask ales could help, The rules do say the beer has to be at least 5% alcohol, which rules out most by normal tipples. So perhaps Badgers Golden Champion, which gets to the 5% mark without being too heavy.
I don't where your local bike club is. I know the club I belong to in Bath, recognised the problem with the Sunday "social ride" still being 50-60 miles at a pace some people struggle with. As a result we also run rides on Saturday that are shorter and slower (25 or 40 miles at 10-13mph or so). They are usually groups of about 6 or and people are happy to bumble along with the slowest.
There are two other bike clubs in Bath (that I know about). One also runs slower shorter sessions to bring people on and the other one is the generally more sedate (that's not a dig, they just like to admire the views) CTC.
Don't just rely on the website, e-mail the club and ask. I am sure you will get a friendly reply and good advice.