I wouldn't.
Should be plenty of drivers with Senior shafts out there..
Plus.........
One company's Senior could be another company's Regular.
And a Senior in one model from one company could be a Regular in another model from the same company.....
Not all Senior shafts are the same....
Weight of the shaft is possibly as important
I would suggest that a (good) fitting for a shaft is a highly important (most?) part of a driver fitting - so if you can, and you’re buying new, get a good fitting focussing on the shaft
I think they might have to stop using "senior" as a designation as it is so offensive and not accurate, because age does not relate to swing type necessarily.
I don't think my swing is good enough to have a fitting. Last year I moved from steel to grahite shafts and found it much better on the hands, less pain.
As I'm 57 now with a slow swing, I just assumed senior flex was the way to go.
I think shaft weight may be more important for most average players, especially as Father Time starts to kick in. A firmish but lighter shaft might work well for a decent player who can square the face but is struggling to get the clubhead back to impact as effectively as he previously could.
Definitely agree a fitting is the way to go especially if you want to try several brands. Explain what you are looking for and make sure they have suitable shafts in stock. Personally I would go to a decent fitting centre rather than the well known high street stores