Same for me, and my account is almost a decade old. I think it depends a lot where are you from and the kind of activity, as i read stories of people being asked to register a number out of nowhere. Many servers requires you to have it tho, due to spam protection. I just don't talk on those.
If your account is a decade old, and you registered at 13, you're now 23 and they don't need to verify you're older than 18. If you were younger than 13, they might be required to delete your account.
It’s tragic but I have the “verified” setting turned on my public server because it’s literally impossible to stop a determined spammer with the tools Discord has. They can make new accounts faster than you can ban them, and there’s no like “IP ban” equivalent
Discord bans are IP bans by default, but new IP addresses are cheap. Even phone numbers are cheap for a determined spammer.