So in the bestiary there are many monsters which are variable according to various factors. Particularly, I'm talking about dragons which have so many different statblocks for all their different ages and colours and so on.
Now, I understand that the statblocks for all the dragon sizes and ages and colours are not in the bestiary book, as it would fill quite a bit of pages. There is not really a space issue in the reference document though so why not fill in the stats for all the ages of dragons there (Wyrmling, Very Young, Young, Juvenile, Young Adult, Adult, Mature Adult, Old, Very Old, Ancient, Wyrm and Great Wyrm)? It would be a lot less work for a lot of GMs to implement dragons (and other monsters that varies in similar ways) if these stats were precalculated and didn't have to be calculated manually by following the rules of dragon age progression.