en.wikipedia.org/wiki/Oldest_McDonald%27s_restaurant

This sentence is inaccurate as written because it omits the crucial qualifier still operating/surviving. McDonald's own FAQ states that "The McDonald brothers opened the first McDonald's on May 15, 1940 in San Bernadino, California." That predates the Downey restaurant, which the article itself says opened on August 18, 1953.

A preservation source focused on the Downey site, the Los Angeles Conservancy, describes it more precisely as "the oldest McDonald's still in operation" and also says it was "the World's oldest remaining McDonald's" by 1994. So Downey is historically significant as the oldest surviving/operating McDonald's, but not the oldest McDonald's restaurant in absolute terms.

In short: the claim is false because the first McDonald's was in San Bernardino in 1940; Downey is the oldest one still operating or remaining.

This infobox label is misleading because it presents the restaurant as a property on the National Register of Historic Places. But the sources for this site describe a different status: eligible/determined eligible for listing.

The Los Angeles Conservancy's page for the restaurant lists its designation as "Eligible For National Register" and says the stand "was determined eligible for listing in the National Register of Historic Places" in 1984. An official National Park Service CRM Journal article is even more explicit, stating that the 1953 Downey McDonald's "was determined eligible for listing in the National Register on January 19, 1984."

Those are not the same thing as being formally listed. So presenting the site simply as a "U.S. National Register of Historic Places" property overstates its status.