I retired earlier than I'd expected to, at 57. The biggest hurdle for me was that the increased in the SPA meant that there were fewer women of my age not working, so the people I socialised with (during the day at least) were a decade or so older. Obviously, over time that changed, and now I am at SPA myself. I found plenty to do - I took a course of study for the first couple of years, and did some consultancy work on a very part-time basis until I was 66. I am something of a 'joiner', and tried many local groups to meet new people, as well as starting up a couple.
I agree that psychologically it can be difficult to go from being 'a something' (whatever it is) to 'an ex-something' which can make people feel less relevant. I think the part-time work helps with that transition, but it wears off anyway, and I really like the fact that my retired social circle is very mixed, and it doesn't matter in the slightest what anyone did at work.
Also, you may well find that you spend less than you did at work. You can wear what you like, and don't have to pay for coffee etc unless you want to, or contribute to leaving gifts and baby presents. There will be no commute either, and you can spend longer cooking so might find that your food bills go down.
Finally, try to enjoy pleasing yourself. Not setting the alarm never gets old for me, as does eating when I'm hungry instead of when I can fit it in between other things. And remember that you don't have to leave anything until Saturday
. Tuesdays probably work just as well, and are less likely to have queues - that took a while for me to realise
.