If you exist, your future self never kills you.
Stop thinking of it from your current self's perspective, your future self is still existing in the future. You don't have to grow up and go back in time to kill your young self or prevent your birth, if that's what was going to happen, it would already have happened.
Think of the past, present, and future states running together- not coming after or before each other.
Your physical self limits you to only perceiving the present, that doesn't mean your future isn't happening right now or that the past never happened.