I was Wondering what is the gold rule for retiring characters how much gold does start with when creating a new character
Under "Creating New Characters" in "Visiting Gloomhaven" it's specified (emphasis mine):
If a player starts a character above Level 1, they should go through all the steps outlined on p. 44 for each level increase in sequence, up to and including their chosen starting level. In addition, a newly created character receives an amount of gold equal to 15x(L+1), where L is their starting level. A character starts with an amount of experience equal to the minimum required for their level (the number listed below that level on the character sheet).