Even if you lie and get in, the fact that it is on record with the RAF means that if they do discover it, you are open to a charge of "fraudulent enlistment", with a possible add-on of "providing false information under oath"... remember the part "I swear (or affirm) this information is true and complete to the best of my knowledge"?
I would expect that if they learn that you had been turned down by the RAF that they will want documentation on what you tell them for the reason, and will check with the RAF to confirm the details if you admit it was a medical rejection.
In this case, contact the regional recruiting headquarters and ask them outright... being fully honest. (the regional has less quota-driven reason to BS you than a local office would)
In many cases, if approached openly, a waiver may be granted for an older person such as yourself, as presumably you are more mature and safety-conscious than a low-20-something... and with such a long period without incident to show your responsibility, they might just surprise you.