Berenberg_Bank, private bankers since 1590, and Beretta, making guns since 1526, are probably the oldest large companies. There are a few wineries, hotels, and religious goods makers that are older, but quite small. Berenberg remains a successful merchant bank today, and Beretta guns can be purchased wherever guns are sold.
[1] https://www.berenberg.de/
[2] https://www.beretta.com/