As long as you follow the proper regulations for private jets, there is no reason why you couldn't buy and fly a 747. The oldest 747-8 is only ~8 years old. It's not that second hand ones aren't occasionally offered up for sale, but if you're restricting yourself to the -8, don't expect a lot of great deals.

While it is a feat limited to the ultra-wealthy, it is entirely possible for a private individual to own a Boeing 747. Often referred to as the "Queen of the Skies," a new 747-8 VIP can cost upwards of $367 million before a single piece of furniture is added. Transforming this massive commercial airframe into a private palace—complete with master suites, boardrooms, and sometimes even medical facilities—typically adds another $100 million to $200 million. For those on a "budget," decommissioned 747-400 models can be found for under $25 million, though the maintenance and fuel costs for four engines are staggering. Owners must also navigate logistics like finding airports with runways long enough (at least 10,000 feet) and gates large enough (Category F) to accommodate such a behemoth. Consequently, these "Flying Mansions" are primarily the domain of heads of state, royalty, and a tiny handful of billionaire tycoons who require the ultimate statement of prestige and global range.