When you say that you work out a few days a week, is it cardio only? If so, try doing 20 minutes of strength
training before your cardio
workouts. What happens when we get older is that we lose muscle mass, which makes the metabolism slow even more. Don't change your current workouts, but add that strength training--look up tutorials on youtube on squats, lunges, biceps curls, tricep kickbacks, back rows, (female) pushups, chest presses, planks, crunches, etc.