Is it ok for my child to not be talking by the age of 3yo?

No. Could it be normal? Yes, of course, they may be the infamous "late talker". But by 3y/o, i'd be concerned about at least expressive language. A hearing issue needs to be ruled out also. If he's able to follow commands well, and understand complex concepts, it may be a simple expressive language delay requiring therapy. But a child not talking at all by 18 months is a referral to speech therapy.
No. The normal three year old speeks & understands hundreds of words, speeks in phrases & short sentences and should be understood 75% of the time by strangers. If this is not the case, contact your local school district special services section to schedule an evaluation. A checkup & hearing evaluation are also in order.