Mihailomilovanovic/Getty ImagesI’m about to reveal my age, but trust me: It’s relevant to this story. When I was growing up, my parents gave my brother and me cash. It might have been our weekly allowance or money for a Saturday afternoon at the mall, but whatever we had in our hands was our budget. There was no tapping the phone, swiping a screen, or asking Mom to Venmo us another 10 bucks. Melissa Murphy Pavone, a certified financial planner, remembers it the same way. She recalls counting coins, organizing bills, putting money into a piggy bank, and physically handing cash to a cashier whe...