I am not in the camp that believes the whole young Anakin force ghost, but the Normal looking Sebastian is ridiculous as well.

Exactly how I feel. I don’t think that his younger self is the most obvious form to take on, but it makes a hell of a lot more sense than appearing as a man who never existed. You also pointed out that Luke has probably seen pictures and videos of Anakin, which is something I forgot to mention. Remembering this makes it perfectly clear why, assuming he had the choice, chose to appear in this form.