the age reccomendation for duplo is 2 to 5
Its funny, but I've noticed different sets of duplo with different ages - some say 1.5, others say 2 :shrug:

I love lego, so encourage anyone to buy her duplo/lego for her birthday, but def. agree that you need to clean it up as soon as they are finished playing! DD is getting really good at putting them away when I ask.

I've never thought to look at ebay - shall check it out. I picked up a good amount of duplo at a 2nd hand baby store for $5 which I thought was a bargain.