Most research seems to indicate that planets form around stars in only the first few million years. Many stars have protoplanetary disks at one million years, but they're all gone by 10 million years. The trick for astronomers is to find stars in that in-between age, and catch planets in the act of forming around the parent stars. One star, Trumpler 37, seems to be at that middle age and is actively accreting material at the equivalent of 10 Jupiter masses in a million years.