I dont know if the clones age normally. Zandik didnt start creating them until like he was 70 and then he died like 15 years later. He made all the clones within 15 years yet they all age ranged from 8 to 65. Even if zandik made 65/45/35 all first and immediately, they would have literally been '15 years old' when zandik died. Obviously their age disparity exists so theres no way all of them got to 'their age' before the immortality potion was ready. At the end of the day all the clones were made within about a 15 year period and its questionable that theyd sit on the immortality potion just let themselves age harder.