For me, it's all about enabling choices. This will probably involve early retirement in later 50s but also working very very part time ffrom 50s.
Strong saving and frugality mindset. Paid off mortgage by 40 by not having over-stretched early on and being satisfied with 3 bed semi and not moving onto more expensive property although we could have easily got the mortgage for it. Perfectly happy with the house we have.
From 40, able to save much more as no mortgage, which resulted in the freedom to choose independent schooling (in my mind, this stuff doesn't all have to about retirement but about having financial choice to do the things you want...in our case this was much sooner) plus also saved enough to to get a BTL outright.
We have the benefit of being in defined benefit pensions which although we are both in pretty average public sector jobs, will give us pensions of about £20k each year which a re index linked. Someone on another thread, said that to get such a pension from a defined contribution pot would require a pension pot of over £1m. It shows how good the defined benefit pensions are.
We will be able to take part of our pensions at 60, which remain in the old final salary schemes (which needed in 2015 but will actuall run until 2022 following the McCloud decision) and the rest at 67 under career average method, along with our full state pensions of £9k each.
We don't intend to take these pensions early as that would mean they are actuariaally reduced. Therefore we need some funding for my early retirement and to bridge the gap from 60 to 67 for myself and DH from a bit later (he likes work and wants to keep going longer) for about 3/4 years. These gaps will be bridged by my DH still working and the fact we can live off one income, along with money which can be released from a private pension (accessible from 55) and money invested in ISAs, plus a decent lump sum which will come at 60 as part of the final salary pension.
Some level of frugality has been shown by keeping cars until they are old, plenty of holidays but inexpensive ones mostly, limited amounts of DIY, not being very interested in lots of clothes or consumer gadgets and just being generally careful in terms of switching utility, shopping around for insurance, keeping a lid on the food shopping bill and having a sense of buying value rather than cheap. These frugalities have allowed some extravagances in other areas, which people with our salaries might not usually expect...we've had the independent schooli g for our children, the odd special holiday, plus bought a 2nd property which we let out and now generates a decent additional income for now and for retirement too. We have been careful and had an eye on the long view, but did also benefit from the fact we bought our first property in the late 1990s, when property was expensive but affordable with careful saving, and then have seen significant house price increase. By not trading up on a regular basis, the mortgage remained low relative to current house prices and was a big boon, that we cannot take any credit for.