Best at what? This is quite a statement. What do you have to back it up and that describes exactly what they are best at? I don't think you can support this statement, and I am quite certain you can't support it as a universal statement.
No, it is not an opinion, it is a universally accepted fact that maestros perceive and direct music even better with age in normal conditions...
Then why do they almost always do their best, most memorable work in their earlier ages, at least the ones who bring forth new interpretations on classics? One could equate your statement to nothing more than good pattern matching. They have conducted said piece so many times, and with so many orchestras, that they instantly recognize when something is out of place, at least to their liking. However, we are talking for the most part what could be somewhat gross variances. However, their experience cannot overcome very real physical deterioration. They won't hear those quiet passages quite as well, or how well a quiet note tails off.
But lets walk back your statement I don't think it is universally accepted that maestros perceive and direct music even better with age. I think you will find that statement hard to support. I think what you will find, is that the best conductors, are the best, no matter what age they are at. The remaining conductors at an advanced age are remaining, not because they are better with age, but because they are better period, and always have been. Did know there are studies into how long conductors live. They seem to have long average lives.
