20 years. The data shows that 10-20 years old houses are the most popular, while old houses over 30 years old have the lowest transaction activity. Houses with 10 years old are almost the same as houses with 20-30 years old. Then, what is the reason for the low turnover of old houses in 30 years? Isn't the old house worth buying? In fact, from the dictionary data of shell real estate, the old house has its advantages.