One thing I didn't see mentioned that helps some aging people (I'll be 70 in the summer) is increasing the "daylight" around the front sight, i.e., going with a narrower front sight (e.g., a 0.125" width instead of a 0.140" width). I'm one of those very near-sighted people, and while youth and good glasses helped for years, 'tain't so any more. I agree with what several others have said - - - try a red dot. There are quite a few to choose from; that's both good and bad news. Features differ. Currently, the Trijicon RMR is perhaps the best in terms of durability and battery life. Perhaps the favorite combo is the 3.25MOA dot in the RM06 model. Others like the larger 6.5MOA dot. The Delta Point Pro has a larger window (and footprint) and much shorter battery life (weeks/months as opposed to years on the RMR). Aimpoint is poised to release a new, sealed (waterproof) red dot that has a lot of interest. It has +/- the same footprint as the RMR, but is a "box" so volume-wise is considerably larger. Perhaps the biggest issue is that, as the red dots continue to evolve, and one leaps ahead of the other, is that the differing base mounts result in incompatibility. Unless, of course, you have a mount with interchangeable plates, such as Glock's MOS. So there's not one right answer for everybody, and it's a moving target. But red dots are probably the future standard, and they'll only improve (size, ruggedness, lower cost, etc.). For now, for a carry gun, I'd vote RMR.
