There is no definitive answer to exactly how old a baseball card needs to be in order to be considered valuable, as there are many factors that determine a card’s worth. Generally speaking, the older the card the more valuable it tends to be. Here are some guidelines on age and value:

Cards from the 1880s through the early 1900s – These are considered antique cards and any card from this era that is in good condition would be extremely valuable, possibly worth tens of thousands of dollars or more. We’re talking about the oldest baseball cards ever produced here from the early days of the sport. Even poorly conditioned cards from this era can fetch thousands due to their historical significance and status as the original baseball cards.

Cards from the 1910s through early 1930s – This era saw baseball cards really start to take off in popularity as bubble gum companies like American Caramel began inserting cards as incentives. Key rookie cards start appearing that are now worth huge money like Babe Ruth from 1914 and Honus Wagner from 1909. In top grades, these classic T206 era cards can sell for over $1 million. Cards even in somewhat worn condition from this time period tend to start at thousands of dollars or more due to their age.

Cards from the mid-1930s through the 1940s – Production was interrupted during World War II, so cards from the late 30s and 40s can be quite scarce and hold significant value. The Goudey and Play Ball brands were popular and rookie cards of Ted Williams, Stan Musial and Bob Feller from this era are worth many thousands apiece for high grade specimens. Generally, well-preserved cards start at hundreds of dollars from this timeframe due to their relative rarity.

Cards from the 1950s – The post-war boom in baseball card production began, cranking out products from Bowman, Topps and others. Rookie cards of legends like Mickey Mantle are key from this decade. These vintage 1950s cards tend to start at hundreds of dollars in top condition as they push the lower boundary of what’s considered “vintage” in the hobby.

Rookie Cards from the 1960s – This decade saw the sport explode in popularity alongside the arrival of superstars like Willie Mays and Hank Aaron. Their rookie cards from the 1950s are very valuable today. Other 1960s rookie cards like Sandy Koufax and Roberto Clemente also gained value over time. 1960s rookie cards grading highly in museums condition can start around $1000-$2000 each on average.

By the 1970s – Production absolutely flooded the marketplace in the 1970s, making cards from this decade less scarce. Certain key rookie and star cards still hold value today, and can start around $100 or more if in top condition. Iconic rookie cards like George Brett in 1978 are usually several hundred dollars even in excellent shape.

The 1980s – Considered the “junk wax” era with ultra-high production levels. Most common cards barely have value today. Certain premier rookie cards like Ken Griffey Jr. from 1989 and Frank Thomas from 1990 have still gained appreciation. $50-$100+ in gem mint is often a basement figure for their top rookies.

Early 1990s – Last true “vintage” cards as technology ushered in the modern collecting era. Rookies of Chipper Jones, Piazza, Jeter have become valuable futures investment from 1991-1993. $50+ is typical for their top rookies grading sharply.

In summary – the older the card, generally the more valuable due to its scarcity, historical significance and importance as one of the earliest obtainable specimens from that player’s career. While there are always exceptions, as a basic guideline most collected baseball cards appreciate substantially in value once they reach 50+ years old. Condition also plays a huge role, as the finest quality examples are usually worth exponentially more than lower graded copies. By understanding these aging trends of classic cardboard, collectors can better identify value among their holdings.