A mom knows her child better than anyone; even better than the father knows his child! Never forget that! Now, 16 months is not too young. If this child knows how to take off his diaper; he knows how to give paper, flush and enjoys being with you in the bathroom; then what are you waiting for? Forget what the grandmother says. He's your child so you already have the upper hand in knowing him. It hurts nothing to begin the training process. In the moment, my children (2 were boys, one girl) were communicating, obviously understanding and able to follow me to the bathroom, they were started on the potty. Once you remove the diapers, do not use Pull-Ups or any type of diaper-like coverings even at night. Put plastic sheet cover on the mattress, under the sheets, to protect the bed. BUT by all means, do not confuse the issue by using diapers at night and training during the day. It's the only way to send a clear message to the child. Be consistent! No need for any rewards other than praise, hugs, kisses and most of allowing the child to participate in his own training by teaching him how to empty the pot into the big toilet and flushing down the pee-pee, then washing his hands! Oh yeah, let's not forget lower the seat cover before the flushing. BOYS are never too young to learn they must lower the seat cover! lol....
It will all go smoothly and your little one will be trained in no time! You'll see it with your own eyes just how ready he is now. Have fun with it. Potty training should be a fun experience for you and your child; never a stressful one.