By Paula Skaggs Summer is festival season in Chicago — for proof, look no further than last weekend’s Lollapalooza, during which thousands of suburban teens descended upon the city for four days of music, sunburns and body glitter. In return, most residents avoided downtown like The Wiener’s Circle avoids ketchup. But what about those mid- to geriatric millennials (read: anyone over 30) still capable of staying out past 10 p.m. — is there still a place for them at the city’s largest music festivals? Of course there is — with or without the body harnesses. (Note that the Gen Xers are already th…