My manner of life, from my youth
That is, his conduct and deportment, his behaviour among men, from the time that he was capable of performing religious exercises, and of knowing the difference between one sect and another, and of being observed and taken notice of by men:
which was at the first among mine own nation at Jerusalem;
for though he was born in Tarsus in Cilicia, he was very early brought, or sent by his parents to Jerusalem, where he had his education under Gamaliel; so that the first part of his life was spent in Jerusalem, the metropolis of Judea, and among the Jews there; the more learned and knowing part of them, Gamaliel's pupils, and the wise men and their disciples: and his course of life must be well known to them, as he says,
this know all the Jews;
that had any knowledge of him, and conversation with him.