my husband has a huge record collection, of which i should listen again. seems i can never find the record player with the advent of cd's. but, i have to get into the van to listen to the cd's. anyways, on his lp's he has george szell and the cleveland orchestra playing a few dozen things. of course, pitt band - of which he bought every recording. a lot of horn players. some older singers. and a few interesting old russian folk and church (liturgy). some organ music. i really don't know among all this what is older. it all looks old to me.
in my own collection - i would say that the pdq bach is the oldest. followed by 'the fountains of rome' (forget the composer. terrible terrible). i also have, in alaska, an lp of glen gould playing all the bach preludes and fugues. that is probably the most precious item nowdays. one of my piano teachers gave it to me, and probably knew at the time it was going to be an important recording. i wasn't sure i was staying in california - so i left it in alaska. now, i want it back. unfortunately, every time i return - i forget to bring it back. don't want to mail it in case it cracks.