The copyright line doesn't refer to the code, but to the license itself. The time span does not determine until when the copyright is active, but during which time span the copyrighted subject was created and/or modified. This is not relevant here.
You are not free to use the code in any way you like: You have to adhere to the license which you linked to:
- “The origin of this software must not be misrepresented, either by explicit claim or by omission.” – I would interpret this such that you would have to mark the sections in your source code taken from Mr. Norvig. Omitting any credit to him would be a misrepresenting the origin of your software by omission.
- “Altered versions must be plainly marked as such, and must not be misrepresented as being the original software. Altered versions may be distributed in packages under other licenses (such as the GNU license).” – If you alter the code (which you intend you do), you may distribute the altered version under any license you choose. However, you are not allowed to present the altered version as if it were written by Mr. Norvig.
In addition to marking the section of code which are based on Mr. Norvigs work, I would think crediting him with a sentence like
Parts of this software are based on code from Paradigms of Artificial Intelligence Programming by Peter Norvig. See <
in your copyright statement would be appropriate.
I am not a lawyer, so you should really consider seeing one.