[Villages PL]

I saw the movie last night and noticed a contradiction. When the boy saw his father's grandfather in heaven, he saw him as a young man. The boy's father thought that was strange so the boy explained that everyone in heaven is young. Then when he saw his sister who had died at child birth, she was about 4 years old. So she got older. She went from 0 to 4 years old. What was the point of that? Why do some get younger in heaven while others get older? Will she keep getting older until she's as old as her great grandfather?