Why I cannot change my Google plus profile URL ?

[Sharp Shooter]

I recently read that now we can have a custom url for google plus like facebook. For example, http://www.facebook.com/Sharp
plus.google.com/Sharp
But I am unable to find such an option in "Edit Profile" --> "About"
As Google Support Says:
http://support.google.com/accounts/bin/a...wer=144414

[Medical Education]

It is true that Google Plus now allows you to have a custom profile URL. But this is true for popular brands, companies and people, etc. Or it is true for the people with lot of followers on Google Plus. Presently ordinary profiles do not see this option.
May be Google also allows this feature for ordinary people in the future.