LewSchiller, I am 7 years your junior, don't live in the mountains, but ride a lot. Height is 6 foot, weight 230. Frame size Large. Medium is too cramped.
For rides 20 miles and under on relatively flat land I use my cruiser. It is 7 speed, 26 x 1.5 inch tires without knobs, and has fenders and a rear rack with a basket on it. I average 10-12 mph on it, and ride it mostly for short errands and on cold days when going fast is not fun. I find it comfortable for distances 20 and under. I have ridden it 40 miles, but found that it is too upright for comfort at that distance. Yesterday I rode it 10 miles and enjoyed it very much. Went for a road bike ride after that as it was in the 40's.

Had a Giant Cypress before the cruiser that I rode quite a bit as well. Good for 30 milers. Don't pin yourself down to one bike and think you have to buy that one. Look at other brands and other designs as you may find yourself on something unexpected.