I'll be 60 next month. When I was younger and tying everything unaided, I never tied a fly smaller than size #20. Not because I couldn't but rather because there wasn't any place I fished that you needed a fly smaller than that
These days I have my bifocals, which are probably 3X or so in the close work, bottom half of the lens. Then I also have a 2.5 X magnifier lens/lamp. Then for really, really small stuff (which for me means #22-24, the size of the dinky olives and trikes out here in the Midwest), I have a pair of 3X readers I insert behind my bifocals.
This gives me (unless I'm wrong in assuming the magnifications are additive) along with the lamp and bifocals, 8.5X total magnification which makes wrapping a dubbed body of black kapok on a #24 trike look like I'm wrapping a piece of of three inch diameter black chenille around a flag pole.
Lots of light too. I have 60 watts in my magnifier lamp, another 100 watts in the overhead, another 150 watts in the 3-way lamp on the tying table and probably another 150 or so in my little krypton-bulbed reading lamp that I position above the jaws of the vise. 460 watts in all. Light is my friend...
Then, sometimes, I'll only use the table lamp at the low (50 watt) setting, don't use either magnifier or the krypton lamp and also take off my bifocals and then tie a fly. It's always fun to turn on all the lights, put my glasses back on and find out what I've made...