Even so, that means he worked on the Astartes with the Emperor - so he was around BEFORE the Great Crusade kicked off. If we say he was only brought in near the end, and was a mere 30 years old by then, he still lived through the entirety of the Crusade and has got to be about 250 years old by the time the Heresy ends.
The promotion track for the Mechanicus may not be the quickest, but being a low-ranking Tech-Acolyte (not even full Tech-Priest!) at 220+ years of experience is ridiculous.
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.