Since there is more to aging eyes than threading flies, I recommend you either get a pair of Hat Eyes clip on magnifiers or a pair of cheap readers.

It's SO nice to also be able to untangle knots, read your watch, tippet spool, or look at a bug. A threading gadget won't help with any of that and I find the Hat Eyes make threading any size tippet through any size fly a breeze as long as you buy the right magnification for you.