When I try to load the mod with space-age disabled, I get the following error.

Failed to load mods: __UltimateBeltsSpaceAgeFork__/data-updates.lua:10: attempt to index field 'turbo-transport-belt' (a nil value)
stack traceback:
    __UltimateBeltsSpaceAgeFork__/data-updates.lua:10: in main chunk

It would be nice if you add the 'turbo-transport-belt' yourself if it is not there already (so that the mod can be played without space-age as well), but it would also require changing the recipe(s) a bit.

You: Downloads space age fork of a mod

You again: Tries to play said mod without spaceage

Also you: Complains about mod not working without spaceage

https://imgflip.com/memetemplate/Bike-Fall

You should make space-age a required dependency then. I've also seen people refer to Factorio 2.0 as "Space Age", so I wasn't sure.

Damn I thought I set all the dependencies but yeah I might correct it or add non Space Age Support