While the given answer is correct, couldn't another acceptable answer be "your father is tall", Suo being the formal possessive adjective? See http://italian.about.com/library/fare/blfare132a.htm

Yes. I think you have a point.

Could this be the same as "his father is high?" Google is telling me "you're high on drugs" is the same-- "alto"

According to http://www.wordreference.com/, “high on drugs” is “fumato” (literally “smoked”), “fatto” (“done” or “made”), or “sballato” (“out of order”, “crazy”). According to the Collins dictionary (on the same Web site) “high on drink” is “su di giri” (revved up; on top of the world). Of course, slang or colloquial expressions change as fast as other fashions, often so fast that dictionaries can't keep up (or leave those expressions to more specialized publications: see, for example, http://italian.about.com/od/slangdictionaries/a/italian-slang-dictionary.htm). Also, what a word conveys in another language often doesn't fit what a literal translation of that word suggests in a foreign language. “High” emphasizes only one aspect of the experience of, let's say, marijuana. Presumably, “alto” wasn't the part of the drug experience Italians wanted to emphasize.