From evil presences (only found while exploring, not whistling) you can find items your level or 5 level req higher. So if you are level 40, you can find items with level 40 req, and sometimes (very rare) items with level 45 req.
From normal mobs while exploring you can find items that are 5 levels lower than you, but generally it is 10.
From whistling, you find basically nothing.
I would start exploring at level 40 onwards if you are looking for drops only, so level 56 is a good time to start as well
