Without posting the details, was 13% that your parents paid a significant chunk of their joint earnings? This is the more important aspect of the current situation, not the percentage number itself.
I wasn't privy to too much of their financial details, but I know the rough price of the house. Assuming we were "average", based around average income for the year we moved there, it was about 40% of the average us income.
Huh. According to this post the payment-to-income ratio now is around where it was in the early 2000s, but is higher than in the 1990s. Both still significantly lower than the 40% your parents paid.