Statute of Limitations is 10 years IF YOU FILE.
If you don't file: there is no limitation. They can collect for all earnings over the course of your entire life.
Citizens have a different limitation than the IRS. The IRS' limitation never expires if you don't file, but your limitation to collect from the IRS, should they owe you, expires in 3 years if you don't file. There is a potential loophole to this in the Codes, but the IRS privately interprets that loophole to apply to amended returns only (I tried using the loophole). As a kid I was dumb and ignorant, and I considered about 5 years of returns as a savings account I'd collect on later. Well, I lost all of those returns because of the 3-year limitation for citizens to collect from the IRS. And I'd have to sue the IRS in federal court and win to get them to honor the loophole exemption on all returns, not just amended returns.