I'm mid sixties now and retired a few years. Single no kids. I absolutely love retirement, and can't figure out how I worked for 40 years! But I did.
Two years pre retirement (early exit), I opted for a three day week. This worked really well for me as it got me used to more free time and also to a reduced income! I had the mortgage paid off anyway thankfully. It taught me how to budget for a lower pension income which reassured me lots as it was easy.
I had savings, so I used that to replace windows, change my car (still using the same one as I have little mileage to do now), change the boiler, and best of all, install a downstairs shower room. I also got rid of the bath upstairs to a walk in shower. I can now live downstairs if necessary and my carer if needed in the future can live upstairs. Future proofed as I have no obvious potential carer if the time ever comes. Future proofing is a good thing.
I keep active and walk every single day apart from Sunday which is my lazy day. A bit of daily exercise is important, even if I don't feel like going out I do. Social interraction is also important but I am not a joiner of things, and am a bit quiet and shy TBH, so I love my own company but honestly am never lonely. Have good family (siblings, nephews nieces, cousins) support which I am very lucky to have.
Everyone is different, some need to be out and about doing things and volunteering or climbing Snowdon every weekend, others are happy not to do that. Do not feel pressurised into feeling you HAVE to be busy. You don't, you were busy all your life!