Once the Tripp Trapp® Baby Set is no longer needed, it is possible to move the seat plate from the highest groove down to one of the next 4 grooves, while also moving the foot plate further down so it can still continuously support the feet of the child. As growth is a very individual topic, there is no guideline for when to move a plate further down, as the backrest should always offer back support, while adjusting the plates accordingly.
For adults or bigger kids that have outgrown the seat plate, it would be possible to remove the seat plate entirely and only use the foot plate as the new "seat". While this is also very dependent on the size of any individual, most commonly the foot plate is placed on the 4th groove for a comfortable fit for an adult. The seat plate can either be stored somewhere, or hidden into one of the lower grooves for safe keeping (while still keeping at least 3 open grooves between the plates to prevent sliding).
It is also possible to remove the bottom metal bar, but this is only recommended if the chair is being used by active toddlers that might otherwise step or jump on this metal bar, as this could damage the chair and/or the metal bar. While the bottom metal bar can be removed if necessary, the upper metal bar should never be removed. The seat area should always be between grooves 1-5, which means the upper metal bar will always be just below the seat, which helps retain stability of the seat plate.