I wondered that it is not an even number and so I guessed everybody has a different CP with the starter Pokémon. And in the case it's always the 13, do Pikachu or a shiny starter have a higher or a lower CP?
My starter Pokemon had a CP of 10, a buddy of mine had his starter with a CP of 14, so it seems that it differs a bit, but not by much.
my Bulbasaur has a CP of 14, and it's CP bar is at the absolute minimum.
I wonder if it varies depending on which you choose?
I think it depends on which one you choose, and also your location, like a water Pokemon would be more powerful near a source of water.