From the start of the game, how soon before we can 2H?
2H like getting a two handed weapon, like level 1-2.
Getting access to a skill that's good with a 2h weapon, from lvl 1-2 probably, and there'll be more you'll be unlocking until around level 30-35 probably, so don't worry if you don't like the first one you find.
Getting access to the Titan ascendancy, from level 20-30 more or less for the first trial, until level 70-75 for the last one i guess, with 2 more in the middle.
To be able to do the full combo rotations, yea from level 30 to 50, when you get access to all the skills, the slams and the others that follow the combo, and when you get enough gem slots to put the passives and make it feel nice, don't be scared if your character feels slow and clunky the first hours, it gets better and better, at least in the first game it did.