I don't use Space Age. I changed my local copy of this mod to do this and it appears to work with Space Age disabled. Mostly.
Would also like to disable or hide basic guns, rifles and all ammo. (Need to keep rocket launcher for another mod that uses it to launch seeds. BioIndustries Mod)
It also appears that Military Science 1 is not hidden.

Example code to hide pistol and ammo:
data.raw.recipe["pistol"] = nil
data.raw["gun"]["pistol"].flags = { "hidden" }

data.raw.recipe["firearm-magazine"] = nil
data.raw["ammo"]["firearm-magazine"].flags = { "hidden" }

Hi, thanks for the feedback!
I was already considering making the mod compatible with non-Space-Age runs, just haven't found the time and motivation yet. Now I have an external motivation! :) Maybe I'll implement it this weekend ^^

"Maybe I'll implement it this weekend ^^" - past me, 6 weeks ago. Oops 😅

Just wanted to let you know that I've started working on it, but then life happened. It's also a bit more complicated than it looks like - I need to make a bunch of decisions about which items to hide, which settings to add, how these settings interact with each other, what's in scope for this mod and what isn't, etc... I'll do that eventually, but I've just not been in the right mindset for that recently ^^'

Thanks for responding. No worries.