You are correct that a lot of them are not super young and only about a third of starting centers were truly threats from deep last year. Only 11 made over 1 a game last year (and two arguably are not really centers in KAT and Reid):
Older (31+): Horford (36.3%), Vucevic (40.2%), Lopez (37.3%)
Prime age (26-30): Porzingis (41.2%), Turner (39.6%), KAT (42%), Jokic (41.7%), Huff (40.5%), Bam (35.7%)
Young (25 and younger): Wemby (35.2%), Reid (37.9%)
Others who have done well in past years: Carter Jr, Reath, Embiid.