3.3 million years old, actually.

I don't think the term Stone Age is inherently misleading. For a start, prehistorians very rarely use it. Instead we almost always talk about its major divisions: the Lower, Middle and Upper Palaeolithic; the Epipalaeolithic; the Mesolithic; the Neolithic; the Eneolithic; the Chalcolithic; or even finer subdivisions. These encompass more manageable chunks of time with more homogeneous archaeological records. But whether you split it up or lump it all into the Stone Age, it's important to realise that these are nothing more than arbitrarily divided periods of time in our broad-brush, relative chronology of world prehistory. They're not supposed to represent stages of technological development or "states of being", so it's not necessary to try and align them to what we think are important transitions.

In a lot of ways they're also anachronisms from the days when we only had relative chronologies. Now absolute radiocarbon chronologies are well-developed in most parts of the world, it's becoming much more common to write about, say, the "7th–6th millennium BCE" rather than the "Late Neolithic". However, "Late Neolithic" is both easier to say and easier to remember, so the relative chronologies stick around as a shorthand and mnemonics.

Now that's not to say that the Stone Age isn't widely misunderstood by non-prehistorians. It certainly is. But I think the most common misconception has nothing to do with the Stone Age specifically, it applies to any system of periodization. Namely, people have a tendency to reify and imbue them with more significance than they actually have. So an arbitrary sequence of periods useful for writing about (pre)history (like Stone Age – Bronze Age – Iron Age) becomes a Sid Meier's Civilization-esque tech tree through which all human societies pass. I think we ought to be better at communicating that this ladder of progress idea has long been debunked, but that's a wider discussion.