P.G.
My son was just diagnosed on the spectrum, and he was trained by the preschool by 3.5 years old. I was actually intimidated by potty training, but the KinderCare near my home did a great job. He saw the other kids going, we implemented pullups during the day to practice pulling pants up/down, then progressed to daytime underwear. Now we just do nightime pullups and he's fully day trained. He's 4.5 and has been day trained for a year.
Don't rush - boys usually are slower at it even without the autism issue. See what happens with the peer modeling - it may make all the difference. Good luck!