"Wenn" also can be used as "whenever", exactly like in your example. Wenn du eine schöne Fraue siehst - whenever you see a pretty woman.

Yes, "wenn" only means "if". English "when" (unless you can replace it with "if" in English) corresponds to "als". There is also "wann" (interrogative and relative pronoun). wenn = used for a general condition that could apply more than once. Mostly used with present tense. als = used for a specific condition that was true at a specific moment in time. Mostly used with one of the past tenses. "Wenn du eine schöne Frau siehst, ..." implies a general condition (everytime if/when you see her), so "wenn" is correct. You can translate it both as "when" and "if" into English.