You're probably right, but the articles I've read suggests that Ford and Edison continued tinkering and working right up to the end. Edison was in his 30's when he invented the light bulb and the phonograph. He was in his 40's when he invented the motion picture camera and made a bunch of improvements to battery technology. I've read stories that Ford was still tinkering with engine technology when he was in his 60's and 70's.
Edison didn't invent the lightbulb by any means. [1] In fact, the lightbulb didn't really have much of a singular inventor - it was a gradual and independent research process. Edison has the credit of addressing the shortcomings in previous lightbulb designs so as to make mass commercial production feasible.
I recently had the chance to view the exhibit on the light bulb in the Smithsonian, and learned something I hadn't known before: the big advance Edison made in light bulbs was a less bright light bulb. Previous electric lights were too blinding to use in most applications. Edison's light bulbs were easy on the eyes. When he helped wire up the Library of Congress, he insisted that all of the bulbs be left bare, so you could marvel in their non-blinding beauty.
