Susan,
You're right on the money with the geriatric population comment. I did some experimenting with cigar pens to see how fat I could make the bodies before I thought they were ugly (as a side benefit, I also got great practice at taking apart cigar pens).
Surprise, I had a few with me to show as a joke and a woman offered to purchase one - she suffered from arthritis and could not hold a pen, but the fat cigar fit her hand perfectly and allowed her to write without pain.
Your fit and finish are good looking; unless you're looking to start selling what you make, make the diameter of the pen to satisfy you. Main thing is to enjoy your time at the lathe and keep trying to get better.