As others have said, each kid is different. I have three and one was well past her 4th bday before being dry at night. She was also a wonderful sleeper! My others were dry at night as soon as they were dry during the day. They were all done with dipes during the day at 27 months. Night was just a different story.
If you don't want to spend money on night time diapers or pull ups, get reusable ones! First, they save you money. Second, they feel wet so your child will start to feel wet and wake himself up. Third, it saves you all the sheet changes. For my daughter, she would finally start to feel wet and wake herself up to take off the diaper. Eventually it happened more and more until she was staying dry at night. Look into Overnight Undies by Mother of Eden. For my daughter's full pees, they worked great.
Some people feel getting a child up to pee in the middle of the night just teaches them to pee during their sleep, since they're not really waking up to do it.
Don't push it or worry. This is totally normal.