I talk to retired people all the time. Some of them wish they had never retired. Some are content in their retirement.
One of the differences between these people is health. Healthy people are happier — there is an insight!
However, your health is not under your complete control. Your hobbies are under your control.
Retired people who have hobbies that deeply interest them are more content. The sense of purpose that employment gave them can be replaced by a hobby or a number of hobbies.
If you are considering retirement you should also be considering how to enjoy it — time to consider if your hobbies are going to keep you happy in your retirement and if not, time to find some new ones.