"If you meet the eligibility requirements, you can get a custom URL for your Google+ account or page. This means you can choose one of the custom URLs Google preassigns to your Google+ profile or page. Depending on the preassigned custom URL, you may also need to add a few letters or numbers to make it unique to you," explains Google.
For profiles, you need 10 or more followers, an account that is 30 days old or more and a profile photo. For pages, you need to link your page with your site or use Google+ Local and verify your local business.
Pages get Google+ URLs that are based on the site's URL. I got google.com/+GooglesystemBlogspot, but I haven't enabled it. Maybe Google will provide more options in the future.
"Once you meet the eligibility criteria, just visit your profile or page to begin the claiming process. If you don't see the option yet, don't worry: we're expanding availability throughout the week, and you'll see the in-product notice as soon as your custom URL is ready," informs Google's Otavio Silva.
{ Thanks, Tolis Nubis. }