Hi Sharon and welcome to the site,
I agree with the "other" Sharon that you can be diagnosed with MS at any age and I think you're going to see older people diagnosed with MS more often in the future.
Who knows why age 40 had been considered as the upper limit for MS "onset"? Possibly partly due to the fact that the older you get the more likely it is that the patients and medical staff will dismiss symptoms as something age related.
I'm personally convinced that the underlying disease process starts at a similar age for anyone who will, at some point in life, be diagnosed with MS (and those who have MS but will go through life without realizing it) and that age of "diagnosis" or age of "onset" signifies nothing more than the age in which the insidious underlying disease process overcame the masking ability of plasticity and became noticeable.
For that reason, I think, people diagnosed at an older age might as easily be comforted that their MS has already proven to be on the slow track as be alarmed that at the time of diagnosis they are already close to the limits of their plasticity, which could drastically lower their chances of symptom reversal and make further progression much more obvious and seem to have taken a more progressive turn.
I think the opposite of this situation is why we've noticed that when the disease process has been stopped/halted in young people who had experienced fast progression, their reversal of symptoms is so dramatic. They are young, when plasticity is at it's optimum, and their progression had been at a rate faster than plasticity can mask. Stop the disease process and with a little time and, in a young person, all that available plasticity can produce wonders.
At least that might be considered an interesting Lyon "brain fart"