Are these sentences correct?

[RoseSpring]

Are these sentences correct?

1- When/Upon growing old, one usually forgets that he was once a child.

2- I'll never forget the days I spent in that place.

[emsr2d2]

Are these sentences correct?

1- When/Upon growing old, one usually forgets that he was once a child.

On growing old, one usually forgets that one was once a child.

2- I'll never forget the days I spent in that place.

If it literally was just a few days, then that's fine. If it's longer than that, then "I'll never forget the time I spent in that place (or there)".

My comments are above.

[bhaisahab]

My comments are above.

"When" also works in #1.

[RoseSpring]

Thanks indeed.