Weight should be the primary driver to determine the board size rather than age.
Our graphical size chart shows the age segments along with an average weight ranger for that age group.
If your child's weight falls outside their age range, just follow the size recommendations for their weight.
Please note, even our smallest board can easily support the weight of adult size skater. Sizing recommendations are for the benefit of the skater finding a board that is an appropriate size to provide stability while remaining easily maneuverable.
If your skater is about to cross into the next size, by all means moving up a size is a reasonable option.