I believe the rule just changed, it used to allow you if you had the achievement for level 50, now if you have the achievement for leveling to 60, you get to use timewalking. If you played a long time ago you and had max level characters you may still have the achievements for 60,70,80,85,90,100,110 and this applies account wide. This is how a free to play account can still get timewalking if you have another account on the same b-net ID, activate one of them and level to 60 and all the rest get to use timewalking. I like to multibox 10s and 20s so I have toons spread across many different accounts, some vet and some f2p.