Well, let's see here...
Ray Smith was the name of Jack Kerouac's character, and he began writing the novel sometime in November of 1958. Being born on March 12 1922, this would have had Kerouac's character aged 36 at the time it was being written. However, the events depicted in the book took place prior to being written down, such as the climb up Matterhorn Mountain, which took place two weeks after the reading at the 6 Gallery, placing it somewhere in the area of October 27th, 1955. Meaning Kerouac's character would have been about 33 years old during the story.
There are a number of things to consider when stating the margin of error here, however. For example, he COULD HAVE wanted to depict himself a bit younger for one reason or another. And let us not forget my less-than-satisfactory math skills.
Hope this helps.