Can DKs tank at 58 now?

[:1]With little to know threat problems? also, is the starting gear good for tanking?
DKs are amazing at everything right out of their starting area. The gear is fantastic for both DPS and tanking. In fact, right out of the gate, you should be able to 2-man Ramparts with a good healer.
DKs have always been able to tank at 58. You'll probably be doing the most DPs too.
but i heard that dks dont get the best threat talent until like the mid 60s
You don't get Dark Command, the taunt, till 65. You still have Death Grip which is also a taunt but long cooldown.

Truth is with Heart Strike, Blood Boil and Death and Decay (at lvl 60) you should have plenty of AoE threat. As mentioned DKs start with very good gear so most times you'll easily outgear the dps, only BoA twinks could be competitive.
I tanked to level from 60-80, granted it changed a lot since then but I'll say that it only starts to slow down around 65, but it'll still be fun as hell.

Now, I will say that the recent(massive) tanking nerfs and the weirdness of our class right now will hurt you, but it's not going to make it impossible.