How Old is the House?

Gabbo and Hadar were looking forward to buying a house together, and finally found one with a beautiful backyard, plenty of bedrooms, and a grand tree right in front of it. They asked the owner how old the house was, and this is what he replied:

"I planted that tree when the house was built. It was 7 feet tall at that time. It has been growing 3 feet each year, and finally at the end of recent year, it was four times its original height."

"But how old is the house?" asked Hadar.

Gabbo said, "Don't ask silly questions. He’s just told us."

So, how old is the house?