100 years ago, retirement basically didn’t exist. You worked until you couldn’t work any longer and then your family took care of you for a year or two before you died.
The concept of retirement has become much more amorphous. It means different things to different people. It is no longer a date, or a day you go from full-time work to not working at all, or even the end of work.
The first concept to consider in a discussion of “what retirement is” is the fact that you don’t have to work full-time for 30-40 years straight before retiring.
I have no doubt that doing it intermittently or only part-time affects your cognitive and procedural skills.
The better you manage your finances in the first career, the more options you’ll have in your second one.
In fact, some very early retirees are scared to admit they’re not actually working for pay because others look down on them.