My 4 year old got these for his birthday with the idea that he could grow into them.  While he is not building complex structures out of them, once we showed him how the gears work he has spent hours simple gear contraptions and is facsinated by the concept of gears.  With a little adult help, he can build pretty much anything.  I really like the idea that there isn't a "correct" structure that these are supposed to make.  My son also plays with lego for beginners but usually gets frustrated if his doesn't turn out exactly like the picture.  Gears are great building toys for encouraging creativity and teaching the concept of gears.