Ahoy! I had to create an account to share the good news! This might belong in the software issues section... BUT its big enough I think it can live here. The fact that followers don't gain HP or skills when they level has been defining how I play my characters - keeping me apart from my best bud J'Zargo until I felt my current character was at a level I was OK with him being stuck at. PC players could just disable then enable their friends to get their stats to reset. It seemed that couch dwelling console players were stuck with our stasis dwelling followers forever...

The fix?

(MINOR SPOILER POSSIBLE BELOW)

Everyone's favorite skooma cat: Sheggorath (You may know him as Sheogorath!
Simply Wabbajack your follower until they transform into a chicken or rabbit or mudcrab and wait. (I tested this while they were NOT my active follower, and they did unequip everything I had given them) When they transform back they will have HP and skill levels more appropriate for someone who has been at your side since the beginning of your adventure.

So go out their and spend some time with your best Skyrim buddy!

Khajiit got your back!

And how exactly do you determine a follower's HP and skill levels?

this is pretty amazing and lets console users(the other other console) bypass a horrendous bug in the game. casting a spell on time and measuring how much their hp bar shifted would do it.

Hitpoints are fairly easy to determine: how many lightning bolts until dead?