I was fiddling around with the scripts and modding with the same issue in mind, but couldn't find any solution for this. The "CANINV_YR" and "PARENT" parameters are available in the Tech.DBF file in MOD_kit directory but apparently they are not implemented yet. With these two parameters you could set up some preparing techs for Digital Age products and Internet stuff.
One issue is also that when you set the Desktop computer CANINV_YR in the Product_Types.DBF (1980 for example), that somehow messes up the operating system business (since it will always be available, even without the hardware). Even after someone invents the Desktop Computer, the OS business doesn't start selling.
I tried to circumvent this by having the COMPUTER product be a primitive computer with very little demand and necessity, and creating a new "modern desktop computer" product that had more demand and necessity, and that would kick up the computer and software industry in 1990s. Problem here is that the AI is still really keen on getting into computer business, even if there's only the primitive computer available, that has really low demand. I set the modern computer to have way higher demand, necessity and price to make it more lucrative, but the AI didn't seem to be that much interested in it.
I also set the "modern computer" to phase out the "primitive computer" quite quickly with OUTBY and OUTSPEED variables. Also tried the TECH_IMPT variable to give more teching emphasis for the modern computer, but could be that this value is only used by semi-products.
Would be really nice if the devs added some more control over the Digital Age stuff. I'm really interested in earlier starts also, the current state of the game doesn't really allow realistic pre-1990 starts. I think they could be quite simply implemented, since the tech requirement, PARENT and CANINV_YR mechanics are already there.
Some more script features could be imho implemented to enable us to do stuff like add certain types of AIs at certain dates, block buildings/techs/products until certain dates (both for player AND the AI) etc. etc. There are endless options
-Nix