the weight moving to age is an interesting turn of the topic. At the end of next year my son will need to move from Cadet to Junior. If we go from LO206 cadet to World Formula junior or to tag junior / rotax junior I will need to add a good 70+ pounds of lead to his kart depending on chassis that could go up to 90 pounds. It would be better to keep him in a cadet longer but he will age out. I know a lot of S4 guys were not happy about S2 drivers that were much younger bolting on a lot of lead and running against older competition in a class that is a little less competitive. When you compare junior to senior laptimes they are pretty close and could be closer. Seems like keeping kids in junior longer even if they were lighter so they were as quick as senior would not be a bad thing. just as the 48 year old S4 driver may not want to run against the 30 year old S2 driver (weight aside) there are probably plenty of 27 year old senior drivers that may not want to race the 15-16 year old. Perspectives and priorities change as we get older.