I know a lot of people here in Russia, aged anywhere between 10 - 60, who are in some way severely limited in opportunities because they do not speak English. I'd advise learning it as a must - it simply "opens too many doors" to be ignored.

In Russia, in the 90-s people who spoke English more or less decently were so rare in some regions that they were hired mostly for their knowledge of the language. Not sure about Turkey, though.