We can probably figure that in 1985, 17-year-old Marty McFly, 20-year-old Alex P Keaton, and 24-year-old Michael J Fox all looked identical. Even though Back to the Future was filmed in the spring of 1985, but takes place in the fall of that year - I don't think Michael J Fox and Alex P Keaton really looked too different later that year. I don't go with the way Marty looked in the second and third films, as he really would be a little too old to pass for seventeen. So I just go with the first movie. Do you think that, in 1982, when 17-year-old Alex P Keaton started showing up on Family Ties, 14-year-old Marty McFly would look the same way? Even if his face was the same, his hairstyle might be a little different. Alex P Keaton had fluffy hair in the first couple of seasons.

Now, in 1980, 19-year-old Michael J Fox seems like he would've been too old to pass as a 12-year-old Marty McFly - as his voice was pretty deep back then, and 12-year-old boys don't usually have voices that deep. He might be able to pass for 15-year-old Alex P Keaton back then, but I think Alex P Keaton would be a little slimmer.

So, at what point do you think they started to look identical? I know BTTF2 had 47-year-old Marty portrayed with grey hair and not as good-looking, but I think that could also be chalked up to the fact that Marty was pretty unhappy for the last 30 years. I think, in the improved timeline, he would look a little more like Michael J Fox would in 2015.

I think all three would still look the same for now.

What about in their childhood days, though? I'm sure they didn't all look alike then. That's the mystery I'm trying to figure out.

They probably didn't. At least, not at the same time.

Maybe it would be around 1982. 21-year-old Michael J Fox played 17-year-old Alex - and 14-year-old Marty would probably look the same. He might have a different hairstyle, though. Maybe Michael and Alex looked alike for a little longer. I know Michael did play a prepubescent boy when he was 15 or 16. So maybe Michael and Alex looked alike from when Michael was 14 and Alex was 10. It maybe took Marty a little longer to catch up, though.