WHY when the people go to the moon they become old?

Answer 1

Not sure what you are asking. But on the Moon:

The Moon gravity is less than it is on Earth. So by the General Theory of Relativity, time on the Moon elapses faster than comparable time on Earth. So people on the Moon would theoretically age faster than they would on Earth. But...a big BUT...the difference in aging rate would be all but imperceptible.

Perhaps you mean the people feel older when they return from the Moon. That would result because Moon walkers would find their muscles atrophying due to the lighter gravity. So when they get back to the greater gravity of Earth they are weak and have difficulty moving around...like an older person.

Answer 2

When people go to the moon or spend extended periods of time in space, they experience the effects of microgravity which can lead to muscle and bone loss due to lack of resistance from gravity. This causes them to appear older as their physical condition deteriorates faster than it would on Earth. Additionally, increased exposure to radiation in space can also accelerate aging processes in the human body.