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Ichigo becomes a Shinigami in mid-May (according to Chapter 35, page 17). He was 15 at the time. However, Ichigo's birthday is July 15, meaning that he turned 16 before travelling to Soul Society to rescue Rukia. This, however, is not directly mentioned in the story. Since much less than a year has passed in the Bleach timeline, he is still 16 up until Aizen is defeated.

Ichigo is now 17.