If there's anyway it can be done somewhere else on a stronger machine, I would do it. It needs to be minimum 1.5T and with MS protocol (3T would be better).
The MRI I had was on the open one was just as expensive as it was on the closed machine. It was a waste of $1500. If nothing shows up, you may always be wondering "what if..." Or "could it be..." and provide little information for your neurologist. You can get the MRI on disc for your neurologist if you use a different facility.
Now if your neurologist is ruling out a brain tumor, then the open MRI will probably would catch that.
I hope you're able to "MRI shop". This is such an important tool when it comes to figuring out what your neurological symptoms are due to.
The neurologist ordered this MRI at a facility that only has an open machine. It is brand new but 1.2 Telsa magnet.
should I tell him I do not want it performed at this facility due to the poor quality of the scan??
Do not get it on an open MRI machine! These machines are not strong enough for catching most (and sometimes all) of MS lesions. My first MRI was considered bogus by my neurologist. No lesions showed up. The next MRI showed lesions-- even a large lesion missed on the open one.
To answer your question, MS is a clinical diagnosis. If you have symptoms and lesions that meet the McDonald's criteria, and possibly other supporting findings (mimics ruled out), other diagnostic findings, then your age shouldn't be a factor.
Your MRI is an important tool in the diagnosis for MS, but it isn't the only thing. You do need to make sure the MRI machine is at least 1.5T. I'm pretty sure the open machines aren't. Plus, the MRI should be done with MS protocol. If the slices are to thick, it will miss lesions. Contrast is also helpful for the neurologist to determine if lesions enhance (new).
The location of the lesions, shape, etc. are looked at carefully. If you your lesions are mostly in the periventrical or corpus callosum area, like mine are, MS should be considered.
Don't get the MRI on an open machine! It's a waste of money!