You can adjust the building build times by changing the export_descr_buildings.txt file and the unit build times by altering export_descr_unit.

Did you really set it to .05? That'd make a year take 20 turns. Or did you just mean .5 like I and many other have been using?

You might also want to think about adjusting the costs of various buildings and units. Anything other than just multiplying everything by 4 will take some rebalancing though and it could be tricky to get a game that plays well out of it.
The reason of course is that you get income every turn, and if everything takes 4x as long to build everyone will just have piles of cash lying around.

Doing build time adjustments properly would really require making widely varying build times. Knights & longbows might take 2 years, while peasants and perhaps militia really ought to be ready in one turn.

There's also a "slow mod" you might want to look into. It reduces population growth rates. There's more about it in this thread: https://forums.totalwar.org/vb/showthread.php?t=74099