when you pick up the item it's stats are determined by your level then and stay like that forever

or

will the weapon gain strength as you level?

just picked up the Dragonbane at level 24 and am wondering if i should reload a save

and another thing, if they don't level up with you what would happen if i went through the area but just didn't pick it up until i was max level?

I doubt they level up with you. Once you've picked them up I believe they stay at the stats you collected them at. They didn't level up with you in Oblivion unless you had a mod.