mid week tavern/pub gigs are honestly one of the hardest gigs to do, not only is it hit and miss on the nite, you get a variety of age groups and you can never win with song selection. best thing you can do is do a headcount of the age group every now and then, play to what holds the majority, its the best you can do. As for what to play when its the majority of old whales, no idea, check with the venue owner/manager to see what he wants, ultimately hes the one paying you and if he tells you to play certain shit and it sucks then its not your fault. also to the guys who suggested commercial/cheese are on the money as well, try going to a pub midweek and see what they are playing on there nightlife system to get some ideas, im assuming the place you play for doesnt have that otherwise they would be using it for mid week stuff