24 of the 30 ballparks have been built in the last 30 years. The exceptions:
Fenway (1912)
Wrigley (1914)
Dodger Stadium (1962)
Anaheim (1966)
Oakland (1968)
Kaufmann (1973)
Everybody else has had new brick and steel since 1989. The only two that have any right to complain are the A's, as that stadium can't even keep the **** from running out of the toilets (literally), and Tampa. I'm not even sure about Tampa, as that ballpark was built in 1990, and not for baseball in the first place. Any talk of replacing Fenway or Wrigley is likely to cause a riot locally, and Dodger Stadium, Kaufmann, and Anaheim (whatever it's called now) have all seen major renovations in the past 10-15 years. The old stadiums, Oakland exempted, are likely to be here for a while yet.
The Braves left Turner Field this year, which was built for the 1996 Olympics, with the understanding that it would serve the Braves afterwards. The Rangers are replacing theirs after this year. That one was built in 1994. I find both of these situations to be completely absurd. Walking away from 20-25 year old parks is absolutely asinine.
Baseball stadiums will last 40-60 years before you start to have questions regarding renovation vs. replacement. The Polo Grounds crumbled after 40-50 years of use. Ebbets Field was obsolete after about 45 years. Yankee Stadium had to be completely gutted and rebuilt after 1973 (51 seasons). Tiger Stadium required a major renovation after 1976 (65 seasons). They've sunk money into Wrigley to replace concrete falling off of the stadium a couple years ago. Other fields have lasted longer, others didn't hold up
The Mariners got a half-billion dollar stadium in 1999. I don't want to hear a word about how they need money for it.