Every scholarship is different, and the terms are set by the donor. There are some that are open to juniors, but the majority are for high school seniors who will be attending college the fall following graduation. However, you are smart to start looking now because it takes time to research, gather materials and apply. Students who wait until they are seniors often don't have enough time to prepare truly competitive applications. There are a number of techniques that can help to make your search and your applications more effective, so it pays to invest in a scholarship hunting guide or two. Even though you won't be applying for most scholarships until next year, if you spend time preparing now, you'll have much better results.
Mom of an average student who won dozens of scholarships totaling over $90,000 and graduated virtually debt free.