Are the ages on LEGO sets important?

Answer 1

Yes. The larger legos are easier for small hands to manipulate than tiny legos.

Also, the sets meant for older kids are quite detailed and intricate. The directions can be quite complicated.

Of course, an 11 year old could probably build successfully with a set meant for 12-14 year olds. The age ranges don't need to be rigid. They simply give general guidance. A very bright younger child could probably handle a set meant for older kids.