The talking stage? If birds are going to talk, they will, no matter what age they are. My 25 year old YNA has learned new words since coming to me and still repeats some of the spanish phrases that he hasn't heard since he was a youngster. At 1.5 years, a macaw
might be talking already, but he might not. That said, there is zero guarantee any given bird will ever talk, or talk in front of you, even if the bird was a chatterbox in a previous home. He probably will speak macaw though, and likely very loudly,
And he'll certainly say a lot all the time with his body language.
Unfortunately someone else will have to chime in about subtypes of B&Gs, I'm no help there. I do think that 1.5 years is still quite a baby in the sense of mental development, even if the bird is weaned. It may be past the 'prefect completely cuddly and malleable' stage though, and moving towards the next 70 years of its life.
"Should" you get one that is younger? Why is it important to you to get a baby? For me, personally, the answer would be a hearty NO, but that is because I enjoy adult birds far more and don't think I could deal well/happily with the 'teenage rebellion' stage and birdy puberty with all of its stress. I prefer to form a mature, adult relationship from the start. I would not be looking for any bird that's hasn't even reached its teens yet. For you though? It all depends on what you want from the bird, what your goals are, and what you're capable of handling.