That really varies - age when introduced, how often and how the animal has been handled previously. Even how the mama llama reacts to handling (thereby giving the cria it's behavioral cues).
We had 2 rescue llama adults who we knew nothing about their previous lives. Gelded adult males, purchased with a group at an auction. We kept 2 of them ourselves. One was super tame, the other very leery around people. They trained to halter pretty easily..it was YEARS ago, so I don't remember exact timelines. I pack trained them too, and we took long walks.
Our current female came trained - at 8 yrs old she was a retired show llama and rock solid.
We imprinted her cria at birth, and did calm handling of him anywhere and any time we wanted to. He was super easy to halter train and lead. I started working with him on and off since he was little. We did his 1st leading with mom, then progressed to independent leading without her. This was all before he was weaned.
I recommend clicker training. There is a very good website that i learned a lot from by googleing 'clicker training llamas'. My boys are pretty good about being caught and haltered. Just short 10 to 15 minute sessions a couple times per day should make a difference. Hopefully this helps!