Well, checking prehistoric ages of Time Commando maybe gives some idea about unit variety :)

(Note : Pity no one made a successor of Time Commando, even trademark expired , why no one makes a "Time Commando 2" ? )

Another option to consider is to have multiple 'stone' resources related to what they actually do.

"Building" stone is not really the same as "Tool" stone - Building stone is larger blocks that may be more readily found, but collected and used in far larger volumes. Tool stone is however far more specific. Used in smaller amounts, but also collected in far lower amounts.

So building a temple might use up tonnes of building stone, but only need a small amount of 'tool' stone. Creating a warrior with a club or spear doesn't need any building stone, and may only use a tiny bit of tool stone, but an archer would use up a lot of tool stone as it uses arrows.

Expanding on the concept could allow a wider range of tool and building stones that impacted the style (and bonuses) - Tools could be divided into sharps - flints, obsidians, etc, and allow your villagers to create/do things involving cutting, while blunts - hard rounded stones, which allow pounding mechanics, hammers and the like.

Allowing a system with different specific resources to achieve things in different ways could make for a very flexible strategic gameplay, but would require careful balance. Archers and such could have pros and cons compared to slingers. Wood focused structures have pros and cons compared to stone - They're easier to build, but take more to maintain and are at risk of fire kind of thing.

As for description of "Stone age" and farms: Well, "Stone age" is a terribly vague term covering a massive span of technological history. Last I was aware we had the basics of early agriculture in any part of the world before moving beyond a 'stone age' technology level. Farming and such giving the time and energy to gather and process metals.

Limited mining and agriculture was carried out in both time periods.

quite true. different areas advanced at different rates. apparently north africa jumped straight from neolithic to iron age. i'm speaking more in terms of wide range common usage, not first know evidence. I only use "first know evidence" as an acid test for some things considered for inclusion in Caveman 3.0 (like nets and boomerangs) - but not things like agro and smelting.

Oldest known mine in the world:

I do have surface mining for chert, flint, obsidian, quartz, etc in Caveman 3.0, but not pit mines or shafts. and only for tool stone.

feels best with stone, gold or flint as third resource

are you limited to just three types of resources for some reason? seem you need at least 4: food, money, wood, and metal/flint. wood is primarily for construction, and metal/flint is primarily for creating military units. all units require food. and pretty much everything costs money (and time).

but an archer would use up a lot of tool stone as it uses arrows.

that's all i do in Caveman is make flint tipped arrows all the time!

Generally speaking if you want to worry about dates and such you can just google all this kind of stuff. What names the academics associate with what dates in which regions seems to always be changing. All you can say is we have stone construction here at this date, and there at that date, and then pretty much everywhere by this other date.

for example, this appears to be the oldest use of stone construction we've found so far...

https://en.wikipedia.org/wiki/G%C3%B6bekli_Tepe

One case of earliest "mining" was of flint (it can be found as nodules in chalk formations which are easy to dig)

Other cases are 'good' flint rock having people coming from well over 100 miles away to obtain it (and work it locally (into cores) to lighten the load to carry back).

Similar activities for obsidian (a volcanic glass) which was used for weapons (and tools)

Something I only heard within the last few years -- that one definition of the 'new' versus 'old' stone age was that the stone tools were polished (that the skill had increased enough that significant decoration was possible)

Someone said agriculture wasnt 'stone age', but in many places it WAS before metals were significantly being worked

Consider that in pre-columbian Americas (ie - Mayan civilization) there were virtually no base metal tools (but alot of sophisticated copper/gold decorative objects) .

Gold and copper can be found as 'native' (pure) state and be beaten to shape and cut, but were generally too rare/valued to make into tools.