When preparing my futurity horses I believe each horse is an individual and you can't pin point when they will be ready to show, whether a longe liner, a two year old western pleasure horse or hunter under saddle horse.
I am still one of those trainers that enjoys starting the two's myself. I usually want my coming two's in the barn by November unless they are immature or late babies. My approach is slow and consistent. The horse will always communicate what they are ready to do and how they are ready to advance.
I do like to keep in mind longevity is number one priority. Not every horse is a futurity prospect and it takes us professional horse trainers to recognize that and work for realistic goals with our clients.