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The exact age of Christ is not 100% certain. As we described in our other post on the estimated date Jesus was crucified, the most likely hypothesis is that Christ died at the age of 33. If we subtract the 3 years he taught from that time, we can assume that Jesus was baptized by John the Baptist at the age of about 30 in the Jordan River.
The feast commemorating the baptism of Christ is celebrated on the first Sunday after Epiphany, falling on January 6.