Tuck under garage and fire wall

I have read the following code. We have a home with a tuck under garage, built in 1965. In order to sell, it is required by code, required by law to do this?

The 2006 edition of the IRC states the following concerning garage walls and ceilings:
R309.2 Separation Required

The garage shall be separated from the residence and its attic area by not less than ½-inch (12.7 mm) gypsum board applied to the garage side. Garages beneath habitable rooms shall be separated from all habitable rooms above by not less than 5/8-inch (15.9 mm) Type X gypsum board or equivalent. Where the separation is a floor-ceiling assembly, the structure supporting the separation shall also be protected by not less than ½-inch (12.7 mm) gypsum board or equivalent. Garages located less than 3 feet (914 mm) from a dwelling unit on the same lot shall be protected with not less than 1/2–inch (12.7 mm) gypsum board applied to the interior side of exterior walls that are within this area. Openings in these walls shall be regulated by Section 309.1. This provision does not apply to garage walls that are perpendicular to the adjacent dwelling unit wall.

A buyers inspector might very well report the lack of fire separation in your structure. I would.
It is up to the buyer to determine what happens with that information.
We inform our clients. We do not enforce codes.

In my area the requirement is 5/8 " Type X drywall between the garage and home at ceiling and walls for a tuck under.

I agree with Mike. You aren’t required to update an existing structure to meet current code, but all inspectors that I know will at least make the buyer aware of it. A fire doesn’t care how old the home is, and it would be prudent for the buyer update the garage to enhance their safety.

Same here as others said