The researchers asked ‘elders’ (according to ‘facts’ such as year of birth and health) if they felt old, what ‘old’ meant to them. They found that there was no necessary correlation between the two (the facts and the perception): some elders were in very bad shape, needed assistance (lived in retirement houses, with nurses, etc.), but they felt ‘young’ because they compared themselves to those around them who were also in bad shape, and vice-versa.
The researchers didn’t talk about mobile phones, but maybe the same logic could explain paradoxes such as elders (maybe those living in retirement houses if we use the same categorization as M. Fernandez-Ardevol) having trouble using mobile phones who perceive themselves as more able/use the phone more often, etc. (because they compare themselves to ‘worse’) than people who could use it more easily but who perceive themselves as not good enough.