I never once had a bit of a problem telling them apart. Their hari color is somewhat similar now, but when they were born, one was blonde curly hair and one had really dark straight hair. One had light skin and the other dark (still do). Oh, and if that wasn't enough, one weighed 8 pounds and the other one weighed just 6. I could tell who was who in the dark!
My brothers though are identical and my mother had to put polish on one toe of one twin to tell them apart. So I have heard of that.
I'd only agree to be 18 again if I knew what I know now!