"What you say about my voice and singing so low, worries me. I used to accompany myself singing but my range has changed. Should I be bothering with guitar if can't get one down in my range."

Sopranos can sing with cellos and basses can sing with mandolins. As long as you're in the same key it doesn't matter how many octaves difference there maybe. This is where the capo comes into play. You learn to play a song in, for example, C but that doesn't suit your voice. Slide the capo up a couple of frets but use the same fingering. Does that suit? Not quite, OK try going up one more. Seems about right? OK, you're now playing in Eb without having had to learn any new or difficult chords.


" . . . . . I doubt I have the mental power and attention span to do it"

It's presumptious of me to tell a stranger something that I haven't always followed myself, but don't talk yourself into failure or just inaction. A new fact once a day or a new chord once a week and by next Christmas you'll be amazed at where you've got to.
(hope that doesn't sound condescending - it's not meant to.)