Probably the most legimate tests/screenings are the AAA and RAADS-R. I'd suggest you to administer them to him, the AAA has a part where a relative should answer for childhood symptoms as well.
With the RAADS-R it is located here:
http://www.aspietests.org/raads/questions.php and gives a chart for comparisons to NT, Suspected, and Diagnosed for both males and females at the end. Essentially the choices are: Always True, Only True as an Adult, Only True as a Child or Teen, and False.
The AAA is a small battery of tests (tabbed at the bottom), it is available for download here:
http://www.autismresearchcentre.com/arc_tests as an excel file. There are other tests on that site that could be helpful.
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The Aspie Quiz isn't a legitimate screening type test, but it is a questionaire full of Aspie traits. If he scored high on it, it would be likely, but it has no standing other than that.
http://www.rdos.net/eng/Aspie-quiz.php . There are other possible indicative tests in this thread:
http://www.wrongplanet.net/postt113459.html