Depends. I used to need at least 2 hrs for my last meal to settle before I could go train. Now I pound a meal & head straight to the gym. I'm pretty careful about carbs prior to a workout - I either feel gassy or cramped for some reason. I do my AM cardio on empty stomach. I also wait on popping my T-rex because I get stomach aches on that stuff w/ an empty stomach within 20 minutes.
Like Sassy said, it depends. I see the salient points as the size and fattyness of the last meal. Large meal, nuff said. A fatty meal is going to be more slowly digested and require a longer interval prior to rigorous exercise.
My personal preworkout meals are always light. Usually 5 jumbo egg whites, and one whole jumbo, very lightly steamed broccoli and pasta, rice, or rye bread with soup. Give that, I'm good to pound in 1 1/2 hours no problem at all.
On ME leg day I dont (cant) eat for probably 3 or 4 hours prior, or it turns into a session of training my sphincter instead of my legs... sorry for the mental picture.