I found it interesting that in almost every picture of US politician Jeb Bush and his son, George P Bush, sitting down side by side, they have nearly the same sitting height and the same head size, but, when they stand up, Jeb is about six inches taller than his son. Both men appear very proportionate. This picture shows that most of the height difference exists in the legs. That, in my mind, shows that most people should be able to remain proportional looking in appearance as long as they are careful not to overdue their lengthening.

Jeb Bush and son George P. Bush; the height difference is in the legs

Jeb Bush is 6'3 (191 CM) and his son, George P. Bush, is 5'9 (175 CM).

It's also worth noting that tall people tend to have longer legs in proportion to their torsos, so a short person becoming average with long legs might not be that proportionate, but an average person becoming tall with long legs might have a greater chance of appearing perfectly proportionate.