Consider what you were doing at this age.
AKSDJFNAWERKNFAK SYLVIE GUILLEM IS FREAKING 19 Y.O. HERE GUYS!!!
But seriously, she’s a little bit rough around the edge compared with the Paquita variation she performed when she’s matured (x). She doesn’t yet have that absolute control of her body although there are some hints - particularly during the Italian fouette - where you can see that she have the facility, that one of a kind body placement that distinguished her among all of the other hyper-flexible ballerinas.
Also I noticed that in this video when she did the Italian fouette, she optioned for the highest degree of extension, while when she’s older, she played a bit in this part by gradually increasing the height of the working leg after each turn, that kind of choice comes due to the freedom that she have since her technique and control is getting better.