The age for Jungkook initially was 21 with Sae being 23 but right now as i think even more far ahead in the plot, i realized in order to avoid more than one time skips i had to change their age. You'll understand the reason as you read on.

So I've decided to change Kookie's age to 24 and Sae to 26. this will be during 2018 itself tho, making them go through their present, same achievements, same adventures and same debut date; its just their ages are older. The other members age also corresponds Jungkook's age with same age gaps.