Most of the press goes to the exciting new planes rolling into service: 787s, A350s, 737 MAX, A320neo—those are the ones you hear most about. But at the other end of the scale, there are planes still safely flying that are older than many of the passengers.
The oldest plane still in commercial service, by the way, is a 737 that went into service 47 years ago with Air California, and now flies for Airfast Indonesia. In between, it's flown for Aloha Airlines, Ohio-based PSA, Braniff and American. Nine of the 10 oldest in service are 737s or 747s; one is an A300.
But are planes that old OK to fly? Some people probably aren't comfortable with the idea, but industry experts say the key is maintenance, not age. Patrick Smith, a pilot and author of Cockpit Confidential, told The Telegraph (UK) that “Commercial aircraft are built to last more or less indefinitely, which is one of the reasons why they’re so expensive. It’s common for a jet to remain in service for 25 years or more.” He also points out that as planes get older, inspections get stricter.
While most of the oldest are flying with smaller secondary carriers, the old birds are not all out of the mainstream. Delta and American have a number of older 737s and 757s, as well as a number of remaining MD80s which are all at about the 30 year mark. The MD80s are on their way out over the next couple of years.
Actually, it appears that the main reason airlines drop older planes is economy rather than safety. Newer planes tend to be more fuel-efficient, to have longer ranges, more seats for the buck and amenities passengers now expect. For an airline with flexibility, a new 737 may make more sense than upgrading an older one; a new 787 or 777 is likely a better choice than keeping the 747s flying.
Incidentally, if you're curious about the plane you're flying, just note the tail numbers (usually near the tail, not on it, these days.) Type the result into a web browser, and you'll find that several services will show you the age, history, routes and most recent flights. Some emphasize flights, others history. Here's a sample to try, a 1999 737-800 for American Airlines: N904AN