We have some that size here in Vegas that were planted back in the 40s-70s. Mulberries, olives, and sometimes figs were yard decoration staples because of how easy they were to grow in our desert climate. There's a steakhouse here called Bob Taylor's Ranch House that is still open after 70 years and there's several of them in the parking lot that were planted back in the mid 50s. They're massive.
Unfortunately, since then, mulberry plantings became rare due to how much males put out pollen and wreak havoc on everyone's seasonal allergies, and were eventually banned in 1991 along with fruiting olives. Existing trees were all grandfathered in as legal, but many folks opted to cut them down anyways due to the leaf litter in winter and pollen output. All the huge ones I've seen are male or sterile. I've read that mulberries can change gender from female to male once they reach a certain age, but I don't know how true that is.
While fruiting trees were/are still legal, the ban also halted all sales of mulberries, male or female, from any local stores. Only now with the advent of the internet and a huge spike in gardening interest as a hobby have fruiting mulberries started to make a comeback.