The main problem why I decided to mark the UL as incompatible w/ SpaceAge DLC is that SpaceAge itself adds new tiers of belts w/ same speed as UL belts. However! If you still want to use it for some reason - you actually can, just unzip the mod inside %appdata%/Factorio/mods (if using Windows) and change the ! in info.json on line "! space-age >= 2.0.2" to ? using basically any text-editor, even notepad would work just fine. This will make the Space Age as optional dependency and you can start playing w/o any problems.
In the future I may (or may not) add some form of work-around, maybe like option to actually use UL belts w/ SpaceAge buy bumping SA belts to even more higher speed.
