It seems your hirelings' level is relevant to yours and that of new random foes at the time you first meet them. Does this cap, say at 40? Anyone know?

I hired Janessa around 39 - my favorite so far.

You can make them leveled-up to your own level using the console.
I'm not sure, but I think I've read somewhere that they max-out at lvl35?

Xbox, here. I'd get the PC version today if it ran stable on Mac/Fusion.

You can make they level to you own level in the xbox to , go to a safe place , save the game and use Wabbajack on them until they transform into somenthing , when the transformation ends they scale to your level.
Hope it helps , and sorry for my English.

Nice tip Baldurs Gate, thank you.

Your English is fine.

Their cap is pending who the are. Some are 25 and some are 35 and 40.

EDIT : I think only one is 81.

Uesp Wikki seems to indicate that the max levels do indeed vary between the different followers. I saw at least one somewhere at level 50.