Your going have AI progression depending on your settings. Just a matter of how you manage how it gains. There are data center that you kill them lower your AI progression. >:(Evil Space Missiles
can be a good way raise it like mad.
If you want keep your AI lvl low plan your attacks how you expand and your settings. The auto progression rate you setup at the game setup can set so doesn't go up or just really slowly. Your overall stratagy and tactics will have major impact on your AI lvl. Like using >:(Evil Space Missiles
may clear your a enemy quickly but then your AI will go x amount faster.
I if you really want keep your ai lvl low scout the systems and find the enemy home planets soon as possible then plan a route to it. Killing the planets you need kill to get there without using >:(Evil Space Missiles
.