We've already begun encoding information in DNA and there are many examples in the animal kingdom of animals born able to walk and use vocal communication; The Kaminoans are already accelerating clones growth and compressing their learning time, it's not a massive leap to imagine encoding a clone to be able to walk, talk and reason. In AOTC the I think the youngest clones we saw out of their tanks were played by Daniel Logan: I think he was about 12..? Doesn't the Kaminoan say it takes 10 years to grow a clone to full size, too? I'm working from memory here, so I could easily have that wrong. What I'm inferring is that they come out of their bubbling tunes looking prepubescent, then rapidly mature to adulthood within ten years.