My first house was built in 1953 and the lumber was old dense hardwood - the floors felt like they were poured concrete. My current house was built in 1987 and there is a hollowness and bounce to all the floors. Inspections of the floor joists in the basement shows they used new growth lumber and while it may be the correct size, it feels much lighter, less dense, and more flimsy than the lumber in the 1953 house.