If it is too big to grow indoors, you don't have much choice - you grow it outside. Will it survive? We have no idea. It is a tropical plant, native to Mexico, Central and South America. This USDA Plant Profile map shows that it grows in the United States only in South Florida, Miami-Dade County. The Lady Bird Johnson Wildflower Center, home of Mr. Smarty Plants, is dedicated to the growth, propagation and protection of plants native not only to North America (excluding Mexico) but to the area in which they are being planted (in this case, Travis County, TX). The reason for this is to avoid wasting precious resources like water and back muscles on plants that have little chance of surviving. You might try a sheltered, sunny area, Since obviously the tree has already cost you nothing to be planted, give it a try, nothing ventured, nothing gained.
Here is more information on Persea americana (avocado) from Purdue Unversity.