Not to worry hun, DH's "father" was grey by his mid twenties and same with another person I know.

Have u tried a proper "all grey" coverage?

Maybe a good trim will help? I know when I used to dye my hair alot (my natural hair looks almost grey so I don't like it lol) that use to happen (it'd wash out quick, even tho it was a permanent) and it was apparently because my hair was so overloaded with chemicals from the dye it wouldn't stick well enough...

Maybe try going a lighter colour? Like light brown/blonde, etc that way even if it does wash out quicker it's not AS noticeable iykwim?

Maybe try like a tobacco brown (or even darker colour) with lots of blonde foils if u don't think ull suit a full blonde?

Maybe try a diff brand of hair dye if u don't already? I used to change em around abit so I dont know if that helps?

Hope I helped Hun at least u aren't going bald so have plenty of hair to play with! Lol