It all depends...what are your goals? When you say older, what age are you talking....20+? 10+? Let me give a scenario here as I am in the hunt for a dressage potential myself. I am a 30+ year hunter/jumper rider whose nerves caught up with her age; I rarely, if ever, jump anymore, but, I have found a love in dressage. As such, I am looking for a fourth level potential. Now, from the knowledge that I have I have two ranges of horses. If a horse has a good base but is not necessarily showing at the lower levels, I want a younger horse; around 6 or so. If the horse has some higher training, let's say, showing at least First Level but pretty solid in schooling second level movements, I'll go as old as 12. The reasoning is that it take time to develop the skills/muscle etc. A 12 yr old with only basic dressage training is not going to make a fourth level potential prior to their 20s and then you are looking at age issues interfering. Horses with some mileage, as my trainer puts it, can be excellent teachers. For dressage purposes, and my own situation, while the horse may have the training and show background at say, First Level, "I" am not ready for first level as yet just due to needing time under dressage work vice hunter/jumper for position etc, but would have a horse who can do the movements and TEACH me how to work first level. By that time I would have the experience necessary to move the horse up the levels and we grow as a team. I can handle a young horse but the question is, do I want to take that extra time...in this case the answer is no. I just don't have the time to train, literally, from the bottom up with a horse that has no base.