can start as early as new borns
mine started at 3 mths cos i bot them when my dear son was 3 mths old
i bot Glen doman's how smart is your baby from a wonderful daddy in mummysg forum, more info @
GD Baby's Programs (S) Pte Ltd
one thing i like about glen doman is that its progressive with clear instructions...touching on various aspects like physical mobility, images, etc
there are alot of flashcards in the market, in fact, you can find them in this forum too , the user name is SMA..he/she is selling flashcards or coordinating bulk puchase...
also, you might want to search for flashcards in ebay...