a previous, now closed, thread asked - "Does a GA airplane operated not-for-hire at night need a beacon?"

it actually had the answer right in that first post - yes, a powered civil GA airplane with a standard category US airworthiness certificate must have an operable anticollision light system for night flight. no, it doesn't need a beacon.

yet farther down, another contributor posted, "There's no requirement for older planes to have an anticollision light, so I don't know what "minimum" you are setting."

i didn't set any minimum. the regs did. here it is, with a bit of the info that surrounded what the original poster provided:

§ 91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.

(a) ...no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate ... unless that aircraft contains ...

(c) ... For VFR flight at night...:

(3) An approved aviation red or aviation white anticollision light system on all U.S.-registered civil aircraft.

the reg goes on to define what specification an anticollision light system must meet depending on when it was installed and when the aircraft was certificated. it does not exempt "older planes" from having an anticollision light system. is there another reg someplace else that exempts "older planes"?