I know this sounds stupid. But hear my points:
- First of all, I know games not starting from age 1 is never meant to be balanced, and it is impossible to do so, in a competitive sense.
- But since TAD (more so for US and Africans, actually Aztecs as well), there have been quite a few civs that heavily rely on upgrade options which give permanent buffs or unlock crucial units. Asians would be totally unplayable without the wonders, for example. Not to mention some European civs now also have options that give permanent buffs.
If I simply want to skip the age-ups and play a fast game spamming units, those civs would be almost unplayable, while some civs would get a clear advantage if they have similar buffs/units automatically enabled. For example starting from age 5 Europeans cannot upgrade their mercs because they skipped the mercenary contractor, but Africans still get the shadowtech.
Suggestion: keep the upgrade button for games starting from later ages, but make them free and instantly completed.