Well, in my opinion, it's never too early to teach them to talk, but whether they will actually talk or not is up to your individual bird. Conures aren't known so much for their talking ability.
Our conure is Franklin and I've always talked to him from the minute we purchased him. He is 9 months old now and he IS saying some words. He says Hello, Good Boy, Chicken Little (one of our tiel's name) and he's trying to say "Him a good boy" but it comes out more like "heia ooh oie?!" and every night he whispers himself to sleep saying "pretty pretty pretty pretty bird, pretty bird, pretty pretty bird."
Conures have a very gruff, gravelly voice often making them some what hard to understand.
My advice is to speak the phrases you want your bird to learn, and repeat slow and clear and one day you might be surprised to hear your little one blurt out a word.
Oh and I found that if I hear my bird say a word or attempt to say a word, I'll immediately repeat it and tell him GOOD BOY!! And then repeat the word again. My birds seem to understand that it was GOOD and hearing the confirmation of the word they spoke they tend to repeat it again.
Amazingly, our two male tiels are the best speaking birds in our home and I think they have a LOT to do with why Franklin is picking up words so well. Our tiels are the "broken record" every day while I'm at work.
Good Luck with your baby, it IS so rewarding when they learn to talk and I'm extremely blessed to have 3 very verbal boys.
Toni