Only US citizens over the age of 21 can petition for a green card for a family member. So, if your sibling is under 21, you will have to wait. Your parents cannot petition for your green card unless they also become citizens first.

If your sibling petitions for you, you would fall under the [Family Preference Category](http://www.uscis.gov/green-card/green-card-through-family/green-card-family-member-us-citizen) which has a waiting list:

> Congress has limited the number of relatives who may immigrate under these categories each year so there is usually a waiting period before an immigrant visa number becomes available.

The amount of time you would have to wait depends on [a number of possible factors](http://www.uscis.gov/green-card/green-card-processes-and-procedures/visa-availability-priority-dates):

> - The demand for and supply of immigrant visa numbers
> - The per country visa limitations
> - The number of visas allocated for your particular preference category