If you apply for N-400 after the age of 31, you don't need to worry about SS registration because you're already 5 years past the point when you should have registered, and hence outside the good moral behavior window.
don’t know if I am reading this out of context, but it is a misleading statement.
What is important is not the age at which one files for citizenship, but what matters is the status of the individual at ages between 18-26. For example, if you want to apply for naturalization and you are 40 years old now and you were legal in the country at ages 18 and 26 and you were not registered with selective service, you will not be eligible not only citizenship but all federal benefits…