Naruto was Hokage during the meeting, Sasuke mentioned that himself. Naruto just becoming Hokage in 700 is a misconception, he became Hokage before that.READ THE THREAD. Sasuke left BEFORE SHE WAS BORN.
Naruto wasn't Hokage then, He only just became Hokage in chapter 700, when Salad was already in the acadamey.
Some people actually think Sakura was pregnant during the meeting, but that can't be possible because Sarada is the same age as Boruto and in The Last we saw a very young Boruto with Naruto before he was Hokage.
So yea, she was probably 3-4 during the meeting.