User blog comment:BlueBarracudas555/Ridonculous Race Contestants Ages/@comment-11883116-20150806230545/@comment-21325751-20150807015922

For me I always thought it was:

June-August 2007: TDI and TDA (Original cast: 16)

February-April 2008: CMTDARS and TDWT (Original: 17)

June 2009: TDRI (2nd cast: 16; Original: 18)

June-July 2010: TDAS and TDPI (3rd cast: 16; 2nd: 17; Original: 19)

Late 2010: TDPRR (4th cast: Various ages; 3rd: 16; 2nd: 17; Original; 19)