The narrator Pip is certainly much older than the child Pip at the beginning of the story. He reflects back on his feelings, and describes childhood in a very emotional way, but from a very adult perspective.
As I never saw my father or my mother, and never saw any likeness of either of them … my first fancies regarding what they were like, were unreasonably derived from their tombstones. (ch 1, p. 4)
As an adult, Pip realizes that he took the imagines of the tombstones and the writing and interpreted his parents’ features from there. Pip describes the incident with the convict as his “first most vivid and broad impression of the identity of things” because it made such an impact on him.
Another way you can tell the difference is that the younger Pip does not talk much, and when he does it is in short childish spurts. The older narrator Pip is quite chatty. He often reflects on his childhood feelings.
Conscience is a dreadful thing when it accuses man or boy; but … in the case of a boy, it is (as I can testify) a great punishment. (p. 11)
In this case, and in many others, Pip looks back at how he thought and acted as a child, and how those events affected him later as an adult. The adult Pip often intervenes in the narrative, almost like he is wishing things had been different.