The martian blueberries (only blue in false color) found by the Opportunity rover in Meridium Planis are formed by slow evaporation in mineral-rich liquid water. They obviously formed early in the Martian history, but do we know more precisely when these blueberries formed?
Let's call them "hematite spherules".
In principle, things on the Marsian surface can last a long time, billions of years https://sci.esa.int/web/mars-express/-/55481-the-ages-of-mars and https://science.sciencemag.org/content/343/6169/1247166.full state that a mudstone sample was deposited before 1.6Gy.
Unfortunately, the answer so far is we do not know. As longs the formation processes of the spherules aren't known, everything is open. If they formed in mid-air during a meteorite impact they may just be a few years old (https://www.sciencedirect.com/science/article/abs/pii/S0032063314000245) (*). But if they formed in a similar process as those on earth they may be older than 3 billion years (https://advances.sciencemag.org/content/4/12/eaau0872.full).