I think your confusion is that you misunderstand the period of 2150 years. That's the amount of time it takes the pergression to move through a zodical "sign" of 30 degrees.

However an age is only 29 degrees long, because there is a 1 degree cusp between each zodical.

However even if that were the case you'd falsely be assuming the birth of Jesus to represent the beginning of the piceain age.