This is a deceptively simple question. Jesus, as one of the Christian trinity, is without age. He always existed, even before the worlds were made, and will exist forever.
Even if we look at his earthly life, the answer is still not clear. Traditionally, he is thought to have been crucified at the age of 33. But it isn't quite that easy....
All four gospels say he was crucified a Friday at Passover; that would make the date (by today's calendar) April 3, 33 AD.
That would make him 32, though, since there was no year 0.
We can go back and ask when he was born, but that complicates matters further. Scholars figured, based on the known times of power of political figures mentioned in the bible when Jesus was born, that Jesus was born between 7 and 4 BCE. That would mean he was either 36 or 39 when he was crucified.