Factual error: Travis begins the movie at 26 years old, and reports leaving the army with honorable discharge in May 1973. His first diary entry just after being hired is "May 10th." In the newspapers at the end he is still 26, and it says that he has been a taxi driver for 6 months. The movie obviously does not take place in winter, and the only months referenced (plus the timeline of a presidential nomination) are June and July. Besides, 1973 would not be the right year for a story set just before a presidential election, unlike 1976 when the movie came out.
Suggested correction: This error is based on the assumption that he had just been discharged. I don't remember anything in the movie to indicate that as opposed to being discharged three years earlier.
The articles at the end of the movie say "Travis Bickle, 26, has been a taxi driver for six months since he came to New York upon leaving the Service where he fought in a special forces unit in Viet Nam" (sic). I think it's fairly obvious from the context too that he hasn't had much experience with 'real life' after 'Nam, surely not 3 years. The original script didn't have this discrepancy, by the way, because the date of his discharge was May 1971, which would account for just about enough months of difficult civilian life to get involved in the 1972 Presidential race.
