Yogic practices have been around for thousands of years, and it is truly incredible that they have managed to survive up until the present day in some way, shape or form. If you really want to maximize your knowledge of yoga and how it is ideally supposed to be done, we would strongly recommend that you go for yoga teacher training. A big part of the reason why that is the case has to do with the fact that this will take your yogic skills to the next level, so you would do well to focus on it at any given point in time.
However, suffice it to say that if you are past a certain age you might not have the physical strength required to go to a prestigious institution like Marianne Wells Yoga School or anything else that is in a similar enough kind of category. That means that you need to figure out what age would be most optimal in this regard, and in most cases we would say that the younger you are the better.
People that are still in their twenties are primed and ready for all manner of physical exertion, and this makes them well suited to the rigors of yoga training. Teacher training tends to be a lot more intensive than basic yoga training, so it stands to reason that only young and fit people can take full advantage of it. If you are too old, there is a small chance that you might end up injuring yourself and this could lead to problems that would be chronic due to their repetitive and impossible to cure nature all in all.