Your son is old enough to sleep all night. The most important things is that he is full enough. Even if he doesnt' seem hungry during the day, and you are on a schedule, he needs to eat more if he is waking up at night.
Offer him more feedings during the day all day long. It's not enough to do a big feeding at night before bed, it must be all day. If he is hungry, he will eat, don't wait for the signs. If he isn't hungry, he won't eat, so don't worry about overfeeding him. It takes a few days for a body to register it is more full, so after about 3 days of feeding hm more all day long, he will sleep much longer or all night long.
He may need to cut out a nap as well. Kids are always changing, so the routines never last long!
The most important thing is the full belly. It works!!! My step sister has 12 kids who all slept through like this. I was still nursing my daughter twice at night at 1 year old when I finally heard this advice. She started sleeping through the night suddenly 3 days later, and my son (a giant boy-tall, not fat) has been sleeping through the night since 3 months old because I feed him all day long. Good luck Get some sleep!