Is the beginning of coming into birth described in the twelve nidanas? The Twelve Nidanas state the cause for coming into birth. 

Suppose we take a look at a being with the name Robert.

If we look at Robert and rewind time backwards to the time when Robert has not yet come into his first birth, can't we see how Robert came into his first birth?

As I see it, the twelve nidanas state that the cause Robert came into his first birth was because he started doing volitional activities because of his ignorance. The first time he did a volitional activity he basically stepped in the circle of the twelve nidanas and destined himself to "never ending" births and deaths. Is this correct?
If we look at Robert and rewind time backwards to the time when Robert
  has not yet come into his first birth, can't we see how Robert came
  into his first birth?


There is no first birth. Samsara is beginningless. But you can end it. Robert is a concept. There's no Robert existing in reality even from this moment to the next, let alone from life to life.