Is there a fast way to power level someone who has no level 70 ( can't join T6 games ) , from 1 to 70?

play the game, it'll be only a few minutes anyway.

5 minute game

Put it on the highest difficulty, have a lvl 70 come through and kill things. Keep Depths lvl 2 is a good spot or you can do bounties.

someone with no prior lvl 70 char can't access adventure mode. Unless they've changed that, which is possible.

Interesting... Can you let me know what you find out to be the fastest plz