67 is way too early for this though. I could get behind making it free from 75 or so (to give people time to adapt and get used to bus travel before it becomes necessary), but the vast majority of people in their late 60s can still drive just fine.
Realistically, however, just flinging free bus travel at people is not enough to deal with the issue of elderly drivers (unless self driving cars become fully rolled-out earlier than we currently anticipate). The main issues are that a) some people strongly associate driving with independence and simply won’t give it up, no matter how free the bus is, and b) the UK is full of areas that are currently poorly set up for public transport; the services themselves are poor and the populations they are serving are too low-density for public transport to ever be a satisfactory solution.
Ideally, we should be building lots of nice airy retirement-friendly flats (balconies, shared gardens, all that kind of stuff) in mid-town locations at high enough densities to ensure that people are within walking/scooting distance of shops, services and public transport stops. However, this will mean tackling leasehold issues; currently retirement flats are often considered a bad bet in the UK as leasehold laws do not govern things like management fees strictly enough. Reforming leasehold to ensure that management fees are fair, reasonable and transparent (and other safeguards) is important.
Unless the UK can make flat living a more desirable option, it’s hard to know how this issue is going to be solved unless self-driving cars become a full solution very soon. Older people need stair-free homes, and bungalow estates require huge amounts of land per person and typically result in people living at very low densities on the fringes of cities, where public transport is just never going to work well enough to be a decent solution. Plus, the UK is generally very reluctant to build on greenfield sites more than necessary; I can’t see this country being OK with concreting over endless meadows to build low-density bungalow estates.