After "when," the simple present is used to express future time. So, the answer is 4. More information here: https://www.ef.com/ca/english-resources/english-grammar/simple-present-tense/ [excerpt] To express future time, after some conjunctions: after, when, before, as soon as, until: He'll give it to you when you come next Saturday.

Definitely "am" is correct here. The "when I..." forces the present tense, though I can't say exactly why. Examples: "When he is older he will be tall" "When she is angry her ears get red" "When you are older you'll understand"