It is clear from Jonas’s memories that there were once other concepts of adulthood in Jonas’s community. It is possible that some of these exist in faraway communities too. It depends partly on your interpretation of the ending. If you believe that Elsewhere actually is a real place and not some afterlife, then the fact that there is music there seems to indicate they might have feelings, and families.
Neighboring communities seem to follow Sameness as Jonas’s does. Since there is some interaction between the communities (we know because Jonas’s sister’s class goes to visit them), we can infer that they are just like Jonas’s. We know that it is very important in the Community for everyone to be the same and not uncomfortable. So Jonas’s people would not interact with them if they weren’t similar enough. Their concept of adulthood is probably exactly the same.
We also know that Jonas’s community did not always practice Sameness. Jonas has memories of grandparents and love, so in the past it seems likely that there were choices and love. In Jonas’s community, adulthood is just an emotionless existence with responsibilities until you get too old to contribute. Children are in training to be adults from the time they are 12, because the Ceremony of Twelve is the last time they count their ages and the last time they are considered children.
In some ways, the concept of adulthood is similar to some cultures in our world. We don’t generally begin training for occupations until 16 or 18. In America, children have the right to vote or fight in wars at 18, but we generally don’t consider them full adults until the drinking age of 21. Children also cannot marry, but the age depends on individual states and is usually between 16 and 18. In other countries, such as Africa and the Middle East, children marry younger. In the Jewish faith, children are adults conceptually once they have their Bar Mitzvah or Bat Mitzvah at 13.