Well retro is popular among the young. What's old is new again and 50's and 60's decor might cut it.
The 70's are popular with the aging boomers but they tend to stay home and aren't big drinkers.
Grills... I don't know. Concentrate on burgers and fries and sandwiches as the young aren't very sophisticated as regards menus.
And tons of beer varieties, not the mainstream ones. Imported and small breweries. And make sure the choice is well displayed with back lit lighting.