Jenny Castillo makes over six figures, owns multiple homes in DC and vacationed in three countries already this year. But at the end of each month, she’s still counting pennies. “Adulting is very expensive,” Castillo, 32, tells The Post. “Yeah, on paper I make good money, but when you factor in debt, cost of living and lifestyle, it’s not.” Even though Castillo makes more than 75% of the US population, according to 2014 US Census Bureau data, she insists there’s not much left after shelling out for rent, bills, savings and her pleasure fund. “I have a separate account just...