John, I don’t know why your stick blender didn’t work. I have several, of different blade shapes and brands. They’ve worked for me.
I understand that what is critical is that the vinegar or lemon juice or acid you are using gets mixed with the egg, thus forming the water-oil emulsion-emulsifier. But I bet it’s possible to over mix these two, or maybe mix with too high a speed (which could deform the molecular protein structure, so mix gently, then quit blending OR pick up your premeasured oil and add it slowly, in a thin stream to the egg and acid.
Do you know anyone who makes mayonnaise? Maybe you could seek out some demonstrations, or coaching or lessons. Probably you have already checked in at you tube university.
About freshness of the egg, I have used very fresh just collected from the hen house, and grocery store eggs which can be several months old. It hasn’t appeared to make a difference.
I will say, though, be mindful of raw eggs about which you don’t know the origins. I am pretty sure that in the USA at least, there can legally be salmonella in commercially sold eggs. It’s easier for regulators to tell us not to eat raw eggs than to require appropriate sanitation in egg and chicken production…. And cheaper for big egg producers if they don’t have to worry about it.
Don’t get discouraged, it’s not that hard to make mayonnaise. You’ll get it.