The only time we use 'olden' is in set expressions such as 'in the olden days' or 'in olden times', meaning 'past' or 'bygone'. This is the only meaning it has, so it can't be seen as a synonym of 'old'.

Thank you~Su.ki. You are so kind.;)

Olden: means a period of time passed, old means the state of now, like these example: I miss the olden time when I was a child. The old man can play violin very well.