It’s not like there are people checking for immortals, I think it would be flagged by a dmv employee or something when they dont believe a clear 21 year old is actually 150. Let’s assume it’s current day im caught and not bring speculation on what the US is like in the year 2139 is like.
The oldest person on record died at 122, and there’s reason to think that there was fraud involved and she wasn’t actually that old. By the time you were in your hundred-and-teens, you would have attention from scientists even if you looked your age. They wouldn’t be forcing you to undergo medical testing if you didn’t want to, but I think they would resort to force sometime in your hundred-and-twenties. If you didn’t look your age, you’d have attention much sooner than that but people would think you stole someone’s identity (that’s what they think the 122-year-old person might have done) and not that you were immortal.
FWIW, scientists who study supercentarians think Jeanne Calment was legit. She answered some extremely detailed historical questions about her village. She was either a walking Wikipedia about the area she grew up, or her claims were real.
That said, most supercentarian claims probably are bogus. They often come from areas that had bad recordkeeping a century ago, had their records offices bombed out during a war, or are generally well known for pension fraud. They’re often very poor areas that tend to have a low life expectancy, and it’s very strange that a real supercentarian would pop up there.
When does supercentarian hit? 100 or 110? Most of my ancestors (grandparents and older, my parents are in their 80s and still kicking) lived to be over 100, Great Aunt Mary made it to 111 or 112. Only one so far that died early was my mom’s dad, and he made it to 92.