Salaries were lower 25 years ago, but not proportionally lower. Where I live now the average house costs about 14x the average salary. My parents bought their house in the 70s for 3x their income. We bought our first house in the early 2000s for 6x our income. It's getting harder and harder.
Ours is around 20% of net income (my income varies). We're mid forties, overpaying (I think it'd actually be about 17% otherwise) and should have it paid off in 5 years, just before oldest child goes to university (assuming that's what she does).