So i have played countless hours already...but my highest level was 14 on the only playthrough i actually finished,and it was a bit rushed.
I started lots of characters,and then i just feel like restarting - again.
I only completed the MQ once,and now i always stop after becoming thane of whiterun.I fear that if i can't stop this i might get tired of skyrim way before i should.

Any ideas on how to fix this?

play arena/daggerfall/battlespire/redguard/morrowind/oblivion

You don't finish the game after you do the MQ.. just saying.

You finished the MQ at level 14?
I'm 53 and have just started it.

Why do you rush?

Focus a character to complete only one or two faction quests or MQ. Don't play a 'do everything' character as those do get boring.

For example I just finished a Nord Warrior who only did the MQ and Civil War (joined rebels).

My next play is a rogue that only does the Thieves Guild and maybe a few daedric quest.

Then a mage that joins the Mages guild and bards college.

Etc. Just focus them toward some role-playing specific factions and quests. Give them some role-playing rules (for example my warrior never picked up alchemy ingrediants and never made a potion).

Do everything else..? You know there's a whole game out there waiting for you.

Well,i guess i will try to make specific playthroughs instead of do everything ones,might just fix this.