Two-Step authentication

Read the document in the link carefully and see what Apple says.

Two-factor authentication is enabled by default on new Apple IDs and cannot be turned off.

If you have an old account (several years old) and recently activated Two Factor Authentication note this section of an Apple support article:

"Two-factor authentication for Apple ID" - https://support.apple.com/HT204915

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"Can I turn off two-factor authentication after I’ve turned it on?

... If you recently updated your account, you can unenroll within two weeks of enrollment. Just open your enrollment confirmation email and click the link to return to your previous security settings ..."

It's a matter of your Apple ID age, not that of when you bought a phone. If you just set up your Apple ID you have no choice. If you have a 15 year old Apple ID like I do, if I were to enable 2FA then I would have the option to disable it again. I don't know if I could keep on turning it on and off though. Apple doesn't talk about that.

It only locks people out of their accounts if they do not manage their account information correctly. Unfortunately people have somewhat casual attitudes toward accounts, kind of thinking it is like 20 years ago when all an account did was give you access to a BBS for posting better cookie recipes. Now accounts can be linked to your entire financial world and need to be taken more seriously.

You can supposedly downgrade if you are within 2 weeks. If you lose your phone, you can get a new phone with the same phone number. Two factor's risks are much lower than the risks of having your account compromised and lost forever that way.

No. You cannot disable 2FA. It's a security feature. You will not be locked out of your account forever should your phone be stolen.