All the ideas about "let's port an idea to an earlier age" ride on the wave of thought inertia. "How could they not have thought about it earlier?!" Such things include steampunk (Victorian era information technology), Ancient World steam engines, your Stone Age flying, etc.
The problem with this approach is less that people did not come up with proper ideas. While this is true to a some degree, a diligent study shows that most ideas were suggested multiple times. If an approach or a device does not take off (sometimes, literally), the reason is some times the lack of demand (people don't know what to do), but in the most cases the lack of materials to implement the idea properly or the missing economic sustainability (it's too expensive to operate). Or everything together.
To give some examples: The lack of civilian supersonic travel is a prime example of missing sustainability. All those almost full-titanium prototype bombers that never went into production scratch at the line of missing or too expensive materials.
Materials are the key
Gliders were mentioned.
Yes, you probably could build a somewhat working glider from your local wood and local fabric. It would be not good enough in most cases.
The balsa wood hat its fame in the early aviation days not without a reason. The duramold and delta-wood (quite complicated, mind you, that's finest mid-20th century tech!) were invented not without a reason. (Funnily enough, some secrets on fabricating these are now lost, because we have better materials now.) And don't get me started on lightweight and durable fabrics, nylon, aviation varnishes and resins.
Technology is hard. Material science is hard. The reason no one basically built a proper glider before 20th century has something to do with missing knowledge of aerodynamics, yes. But also with lacking materials.
A classic old wives tale is about a local idiot, who builds wings 'cause he wants to fly as a bird, climbs the local bell tower and crashes down. The problem is that the wings would be in most cases designed as wearable items (thus having too little wingspan) and that the materials available to the local madman around 17th century are not really balsa and nylon and silk.
Frankly, I fail to see how your Stone Age tribe has access to such materials in such a variety. You can put them where balsa grows, but they'd be like half an Earth away from where the silk worm lives.
And don't even get me started on engines. Basically, anything less than an internal combustion engine has too little power/weight ratio to move an aircraft. A heaver that air aircraft that is.
But proper dirigibles are another, quite tearful story. You'd need proper varnish and material for the insulation. You'd want a hard hull. You need a carcass from a quite good steel or aluminum that is. You'd still need engines. You need a source of a lighter-than-air gas. Hydrogen is highly flammable, hello Hindenburg! You'd still need some natural source of it (or of helium, even harder) or an industrial way to produce it.
Basically, except hot-air balloons for reconnaissance (used in wars in 19th century, if I recall correctly), anything lighter-than-air is too high-tech for Stone Age. And I doubt hot-air balloons too.
What can we do?
All my text above describes why do materials matter, why logistic chains are important, and why we did not have Stone Age aircraft in our history on our Earth.
You could change exactly this. In your alternate reality, balsa trees and silk-producing bugs are neighbours. Or your Stoge Age tribes domesticates damn huge spiders and learns to milk them for web.
(Damn huge spiders need a yet another change of the reality, say, it's damn hot in the Stone Age and damn huge is not really very large. Either that or damn huge spiders have lungs. This, however, needs a further explanation, why do we not have a civilisation of damn huge spiders long before human Stone Age, but I digress.)
Or your Stone Age guys found some alien technology. And could reproduce some of it. Or at least they learned aerodynamics. Throw also in thermodynamics and quantum theory, because why not? (You'd have then Iulius Caesar killed with a laser, like in one very short Sci-Fi story, but that's another point and I digress again.)
Or the same alien ship would have transported tons of natural silk for whatever intergalactic fashion reason. Or, even better, liquid synthesised components of spider web in industrial quantity. That'd be a non-renewable source, of course, but your tribal shamans could (miraculously) learn to produce spider web and spider silk cloth from it. And we already agreed that balsa trees just grow around where the tribe lives. Or they were great hunters making composite bows routinely and hence they have some technology resembling delta-wood using carefully collected wood, antlers, bee wax, goat intestines and what not.
Oh, and as already mentioned, being locked out on a plateau does not help.