Is it worth starting now?

Sure, its fun league with mercenaries from Diablo 2 xD

As a fellow mostly new player, yes.

You're not going to get close to maxed out level as a new player in the next month and a bit anyway. So just play now, get through the campaign and get going to the point you can once the league ends.

In some ways it is better I think. You will mess up things or learn stuff that are obvious in hindsight as you go along, so if you start now you will have some knowledge gained for your next character, with now knowing that thing with your character you might plan to play the whole league with.

And I am not saying it is a bad thing to push through a rough patch of a character because of mistakes you made but in a way it can help to have this deadline of new league as a way to say ok there is no risk to mistakes because I am only planning to play with this guy for a month and not intending for it to go all the way. So you also won't feel like you have to keep going to avoid feeling like you are giving up.