Some people take it well, others not so much. My parents tend to be super chill and are handling retirement very well, my dad can't sit still (tries to do DIY stuff he shouldn't be doing at his age) but he's always been that way.

My in-laws are both just about retired, they are rapidly losing their minds because all they've ever known for the past 35 years is work or taking care of their 4 kids and now they have neither. My FIL doesn't understand how to not be working, he will literally go home to do yardwork in the middle of vacation because he can't take it anymore. All my MIL does is complain about how much he irritates her. Both of them need hobbies and fast.