User blog comment:MrPedroNorris/Gon Condition/@comment-14902757-20151130003828

It was mentioned in the anime that the power lent to Gon was temporary. I believe that the growth he received was also temporary, even though his hair remained long, his body went back to normal immediately after he used that last blow on Pitou's dead body.

You see here that his body shrank back to normal but his hair was still long. Killua's arms here are bigger than Gon's.

So, no. Gon wouldn't have continued to age. It was only a temporary power and physical boost but he went back to normal. For whatever reason his hair remained the same, I think maybe it's still in the process of returning to normal when Palm saw this.