Ask your representative in the US House of Representatives and Senate ... they made the law that limits the sponsorship right to 21.
Franco Capriotti - Senior Legal Counsel - Capriotti International Law – 503-803-0055
SKYPE CONSULTATIONS AVAILABLE - email@example.com - www.capriotti.com
We are not geographically limited ==> Our licenses allow us to represent people worldwide.
You really haven't given us much information.
You're on a work visa? What kind? H, I, J, L, N, O, P ..... etc?
If you're thinking of getting married to a US Citizen (Canadians and Mexicans are also "Americans") and if you're thinking of filing papers for a greencard w/o leaving the US ... then, yes, it takes about 90 to 120 days for you to get a travel and working permit and it is best to 'stay put' in the US while waiting for those papers.