The People of Israel, in accepting the Torah, did not receive it all at one time.
Rather, the process was a protracted one, from the early preparatory stage of the seven Noahide laws to the acceptance of additional mitzvot in Egypt, at Marah, and at Sinai, to the full revelation there that followed.
Similarly, a child raised to be an observant Jew takes upon itself the full yoke of the mitzvot only after long preparation: years of training and the gradual, step-by-step assumption of responsibility according to its intellectual readiness and practical capacity.
The essential point is that living beings do not undergo sudden, complete transformations.
The caterpillar does not become a butterfly in a single act but as a result of a gradual process.
–Rabbi Adin Steinsaltz
From Teshuvah by Rabbi Adin Steinsaltz