In a test there are such sentences:
"When I was little, I shared a bedroom with my sister Catherine. As I was eight years her junior, I obviously
(used to go / would go) to bed earlier than her."
The test says that the only correct answer is "used to go".
I've read in the rules that we can use would "to talk about repeated past actions". Also the rules say that "would should not be used unless it has already been established that the time frame is in the past, while used to does not require this" (http://www.learnersdictionary.com/qa/the-difference-between-used-to-and-would).
But doesn't the phrase "When I was little" set a time reference? Or it's not related to the second sentence? Or it should be in the same sentence? Or maybe there is another rule I missed there?
My question is: can we use would go there, and, if not, why?