2.5 years is plenty good an age to start using chopsticks.
Our children both used them well before 2. We never taught them though.
Beside all the creative answers here, I would suggest a more psychological approach.
We all love to cook in the family, and the little ones would hang around to help in the kitchen when we prepared the food. Often times, some part of it involved using chopsticks to stir, and the kids jumped in to help because they were curious and just being kids. It's all play and learn to them. They naturally picked up the chopsticks and naturally appreciated their intrinsic effective value through use/play.
They also love to eat. We pay a lot of attention to the food we cook, and luckily they loved practically everything we made. We also had special treats nearly twice a week if not more. Somehow, teaching them to use chopsticks never crossed our minds. We never used any training chopsticks, nor spent any teaching time. I particularly think the training sticks are like bicycle training wheels, the longer you keep them on, the more you prolong the dependency and lessen real use.
Make the food so enticing not only in taste and texture but in how fun it is to savor, and the use of chopsticks essential to its enjoyment and your son will get it done in 5 minutes.
You can even create a game, or a ritual, on something really good that he absolutely enjoys. Suppose you encase a delicious and attractive treat inside a jello pudding, and use chopsticks to pick it out as a game. With some simple rule about using the chopsticks to get to the candy -- he'll get it done!