We have all learned the Rashi that states that Rivka was three when she married a 37 year old Yitzchak! This has always bothered me. I can think of a few reasons:
1. Because the actions of Rivka in ch.24 - the sheer volume of water that she shleps, her parents consulting with her - are not possible for a three year old. (And please - don't tell me that human nature has changed or that she was such a tzadeket etc. etc.)
2. Because the Akeida doesn't seem to happen to a 37-year-old.
3. Because it is simply wierd for anyone to marry a 3 year old, let alone an middle aged bachelor. And we treat Rivka as a serious adult from the start.
The basis of this timeframe comes from Seder Olam (a very old Tannaitic work) which links three parshiot: The Akeida - Avraham hearing about Rivka's birth - and Sara's death. And assumes that they take place at the same time since they are mentioned concurrently. Hence, Sarah dies at age 127 which puts him at 37 at the time of the Akeida (when Rivka was born) and since Bereshit 25:20 states that he married at age 40, Rivka must have been 3 years old!
The easier solution would be to simply suggest that the Akeida is not linked to Sarah's death and happened maybe 20-30 years prior to her death. (See Ibn Ezra 22:4 and Ramban on 23:2.) Hence Yitzchak is 10-15 years old at the Akeida; and Rivka is at a regular marriagable age when Yitzchak marries her.
See this excellent shiur which discusses this in detail.