Many people believe that life was better when they were young than the rest of life.
Yes! This is a good way to correct it. I was thinking of it like this:
Many people
would have heard
when somebody
says that say, "Life was better when I was young." It is a common saying among adults. I believe...
You have to also work on your verb tenses. For example, keep all the verbs in the present tense here:
When people
could not cannot find happiness in the present they look back in their past.
Learning verbs are the hardest part of making your English perfect, but you can do it! :-)
Here is another rough part:
Some could have stayed in their childhood itself and restrained to move. I think you should take it out or find a clear way to say what you mean.
:-)