How many years does it take to reach adulthood? I suppose it depends on the situation. In some cases, it’s 18. Other times it’s 21. And some people don’t seem to get to adulthood until they are well into their thirties – or later! Regardless, every person is busy growing up in some way! Even retired people are. The key issue at each age is to give it all you got. Start by knowing God better and learning His ways to a well-lived life.