Depending on how settled down in life, it begins in the early 40s to as late as 50.
It carries on to retirement age or somewhere to the mid to late 60s or possibly even the early 70s.
Middle Age is characterized by when you stop hanging out with younger people and don’t identify with them as much, but relate to your OWN youth (times when YOU were a young adult, college, etc etc). Or, Middle Age can be described as when you are old enough to be a grandparent. Children see you as older than their parents thus an authority figure rather than a cool aunt/uncle/teacher/camp staff person.
Its still an okay age to be. But when people get ELDERLY they start to get set in their ways, forgetful, closed minded and intolerant of things which they had previously been open minded and tolerant about. You can still BE open minded and receptive past 70, but that’s when it, and middle age, usually ends for most people
Middle Age is the age of Presidents of the United States of America