What is maximum length of Destination URL?

On the page that you have linked is stated that URL link can include up to 2048 characters.

A Destination URL is simply the address of your webpage people reach when they click one of your ads. The way it's worked until now is that AdWords ad and keyword tracking relied on the Destination URL, which was made up of the landing page URL and tracking parameters. Your destination URL can include up to 1024 characters.

The length of the url should be about 40 - 60 characters

40 to 60 character and must have keywords

It is the URL address of the page in a website that people reach when they click on ad.