Alternatively does old age have any effect on ability to do those tests?
Vision inexorably deteriorates with age. Your optometrist can draw you the graph.
I am above the curve for my age and can pass the CASA vision requirements without glasses when I'm in a well lit medical consulting room. But I know as soon as the light deteriorates, that I struggle to read easily - ie an IFR approach in cloud. Therefore, I have a $20 pair of chemist reading glasses in my flight bag as well as my prescription reading glasses that I use intermittently for detailed reading. I'm not required to do this, but its safer and I feel more comfortable.
The spare pair don't need to be perfect, just adequate to pass the test. Thus they can be an old pair or, if the cheap Chemist glasses do it, it can be them. Primarily you only need to read something on your lap or on the instrument panel in front of you.
There's a fair chance your local optometrist will bulk bill you on medicare. There's also a fair chance he'll understand the CASA requirement (which is not as strict as some others). Go and see the optometrist. Take whatever old glasses you have, or borrow some chemist glasses and try them out.
Its easy to scoff at the vision requirement, and for a J3 Cub its probably overkill. But trying to read a map in difficult conditions, or an IFR approach plate in cloud or (as I have done) read through an aircraft flight manual after declaring an emergency and being able to read & comprehend clearly takes on new importance.
Once you know what your vision is, then go to your friendly neighborhood DAME armed with the answers before he submits anything to the unfriendly, untrustworthy, irrational, vindictive CASA Avmed.