Comment by judofyr

I imagined that I'm 24 years old and I have a 20 years old brother. When I were his age, he would have been 16 years old.

I also realized that this can be expressed in terms of a two pairs of sibling:

> Mary and Ann are the same age difference as Jane and Claire. Mary is 24 years old. Mary is twice as old as Jane. Claire is as old as Ann. How old is Ann?

This highlights also why it's so confusing:

> Mary is 24 years old. She [Mary, today] is twice as old as Ann was [Ann, past] when Mary was [Mary, past] as old as Ann is [Ann, today] now. How old is Ann?

In one sentence we're comparing past and present ages.