After we appear to die and go to an in between plane

We enter a life and learn. We accumulate knowledge then die. We enter an in between or astral plane. We may choose to come back 600 years later and the world may have progressed far beyond where I was at passing. Are we retarded by 600 years? Did we continue learning in the astral plane? How do we keep the concepts we’ve learned in the prior life? Just an example, I’ve come to believe we recycle or reincarnate. Seems babies have to relearn that? Seems like a lot of repeat learning, is that a total waist of growth?