I love Lego! I loved it as a kid, and I still love it now. The blocks themselves haven't changed, all Lego blocks from way back still interlock with the current kits. There are Lego sets for all ages.
Duplo is for toddlers, they have larger blocks and fewer pieces.
Regular Lego for kids, these would also include the franchised Lego such as Harry Potter or Star Wars blocks
Technic for teens and young adults, consisting of more complex kits and moving gears and more interactive pieces.
and the latest Lego line is Mindstorms... a robotics line complete with programmable CPU, various sensors, and mechanical parts for... well... people that know what to do with it: