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.