It's time to talk to your DM. You clearly have ideas about the general shape of your backstory, but you need to know some things that "everyone in the setting knows" and you need names, places and dates that don't conflict with the setting's plots, or the DM's own ideas for their campaign.
It may well be that the DM will use your backstory to help develop the place(s) your character has lived. For example, if someone in your home village encouraged you to take on a particular career, that's part of a NPC designed. Dungeon World makes a point of delving into such matters, but the idea is applicable to just about any RPG.
Working with you on this is worthwhile for the DM, because it means they can reveal things in the course of play that "your character has known for a long time," but become significant in the light of campaign events. They can also have events that tie into your backstory, but they should not have too many of those, nor drive the plot by them, because it will make you feel like their puppet, rather than a contributor in your own right.