My 82 year old dad has just tested positive for covid. he has had all of his covid vaccines and boosters, and currently just has a nasty cold. i am so worried that his symptoms will get worse. is this likely?

Maybe. The circulating strains are still killing mostly those over 60. Yet some strains attack mostly above the vocal cords, sparing the deep lung damage that the original virus had that produced the worst infections. Peak illness seems to be around day 8 in most.

Yes it is possible, but the large majority of COVID infections remain mild, even in older persons, especially after all recommended vaccine doses. Probably he will do well. He needs to see his doctor and he definitely should be treated with paxlovid, if he isn't taking other drugs incompatible with it. (And many of these can safely be stopped temporarily while taking paxlovid.) Good luck to him.