I remember seeing a piece on TV about formula one racing drivers. They did some multi-task tests, doing the light wall game (press the button which lights up) while answering questions. The conclusion was that it was the ability to efficiently carry out multiple concentration/analytical processes simultaneously which separated the top rank from the also-rans (i.e. the rest of us), plus they were quicker at everything. Unfortunately the general public (us) are not superhuman and we are not able to concentrate effectively on more than one thing at a time.
I do odd-jobs for other folk, and I always have a rule that while I'm in the middle of doing something, please don't start talking to me about another "little job".
Personally I dislike mobile phones (devices) with something of a passion, and use one only when I have to. I wouldn't ever consider trying to use one for anything while driving, but I recognise that I'm in the geriatric minority.
I try to be quite self-critical, and I know full well that my reactions are not as good as they were 20 or 30yrs ago. Anyone who kids themselves that at 60, 70, or 80yrs old their reactions are just as good as a 25yr old is a danger to themselves and others. Recognise your limits and keep within them and you'll be OK.