Farhorizon's advice to measure elbow on seat to fingertips on bars is traditional and useful. You might also consider your back's position. With your hands in your most often used position on the bars, many people (our age and otherwise) find a 45 degree angle in your back measured from the horizontal is a good and comfortable position. If your back goes flatter, you look like a racer boy and put lots of weight forward on your hands and also extend that lower back (but also get your butt muscles helping). Riding for extended time with a back more vertical than 45 puts a lot of weight on your butt and may not feel "right" for longer road rides.

Still, its all so dependent on body structure, torso length, arm length, etc. that its best to take an "experimental attitude" towards most bike position generalizations...but they're a good place to start.

P.S. Back angle when riding may also make narrower or wider saddles more appropriate.

**Personally, I use an aero bar (not for speed) but for the comfort of having one more position....one that totally unweights your hands. Stick with it, generally there's a solution to most cycling problems.