don't you also think it's annoying you can still build swordmen and frigate's when it's nearly 2000??
here's a solution... open the editor, and go to the unit. There select upgrade to, and select with what unit you want the old unit to be obsolete (i did the mid-age ships with the destroyer, and bowmen and swordmen when rifleman arrived). Now here's the trick. Unselect the upgrade unit option to the right.. when the new unit is buildable by a civ, the old units will still exist (but will die eventually, but the trick is that you and the AI can't build these units anymore since they have been replaced by an upgrade. But because we unselected the upgrade unit option, you can't upgrade that unit either, so it will probly die sometimes (or end up in a museum in your capital if you are a pascifist
)
but the main trick is that it prevents the AI from building these units, so that if you just denied him a resource, he won't start building swordmen and frigates against your marines and battleships
here's a solution... open the editor, and go to the unit. There select upgrade to, and select with what unit you want the old unit to be obsolete (i did the mid-age ships with the destroyer, and bowmen and swordmen when rifleman arrived). Now here's the trick. Unselect the upgrade unit option to the right.. when the new unit is buildable by a civ, the old units will still exist (but will die eventually, but the trick is that you and the AI can't build these units anymore since they have been replaced by an upgrade. But because we unselected the upgrade unit option, you can't upgrade that unit either, so it will probly die sometimes (or end up in a museum in your capital if you are a pascifist

but the main trick is that it prevents the AI from building these units, so that if you just denied him a resource, he won't start building swordmen and frigates against your marines and battleships