I was only a couple of months of 70 when I retired. Best thing was not having to set an alarm each night, worst thing was no money being put into my bank account at end of each month.
I thought I had prepared really well for retirement, attend several meetings on this and had a list of local social groups I wished to join. Also took on some charity work. shop and delivering kosher meals on wheels.
Sadly my two best friends were dead, one just before and one just after my retirement. I felt this badly - the three of us had so often planned what we would do together. For two years I tried really hard, joined u3a locally, and other specific interest groups and found none of them particularly welcoming and nobody in any of them seemingly looking (like me) to form new friendships.
Eventually gave up except for one discussion coffee morning each week and a knitting group.
Then I moved to a small seaside town, now nearly 80 determined to have another go. Less than five months there was hit by covid lockdown. Fortunate that daughter who lived there would take her 11 year old out each day (glorious weather),and I would meet up with them in the park or on the beach. When this lifted I joined local u3a and my life changed, This is a large branch with lots of different interest groups each week/month.
I did lower my expectations - no longer seeking new friends, but do have lots of aquaintenances, always somewhere to go to meet up, have some group I can tie each days' activities around.
I think this is the answer, think about what you are expecting to get (and to give) in your retirement. Organisations like u3a and obviously individual interest groups and (for those who can go along this road) the churches can all offer things to do people to meet, outings, etc etc. Some people at these do build new, great individual friendships, other (like me) do not as my friendships were all built on so many common experiences we shared whilst our children were small.
If anyone is quite healthy would definitely recommend some sort of charity work, shops/ hospitals, schools, animal sancturies, parks, etc. are always in need of more volunteer staff, and such volunteering can be a way of using one's own interests and knowledge further.