Complex sentence: All Israelis under the age of 40 who served in the IDF, unless otherwise exempt, are theoretically eligible for reserve duty, but only those who completed at least 20 days of reserve service in the past three years are considered to be active reservists.
Split into simpler sentences: All Israelis under the age of 40 who served in the IDF, unless otherwise exempt, are theoretically eligible for reserve duty. However, only those who completed at least 20 days of reserve service in the past three years are considered to be active reservists.