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.
Buy an infant mortality’s birth certificate every decade and put them into use once the poor tike would have hit 25.
It helps to be in a profession that processes death certification so you can make sure it doesn’t get processed.