Tutankhamun had iron dagger! Meteoritic iron, easier to work than normal iron. Copper & tin for making bronze are both rare, found only in a few select areas, hence complex trade/exchange routes evolved (as already existed for handaxes). Iron by contrast is relatively common. No new techniques needed to extract and work it, but somehow less magical! Technologies were insufficient to achieve the temperatures necessary to melt it, so instead you end up with a grey lump which then needs working with tools (to produce wrought iron). Casting, as used for bronze, is much more elegant! Once iron working technology became established, bronze used more for jewellery eg famous Celtic works. No clear cut off for stone/bronze/iron ages, as all continued to be used for varying purposes at different times.
From In our Time, Radio 4