According to the Oxford English Dictionary and the U.S. Census, you're considered middle aged if you are between 45 and 65.

For those of you in your 50s and 60s doing a happy dance right now, think for a minute. Taken literally, those numbers would mean you might live to be 130.Doubtful.But if you do live to be a ripe old age, wouldn't you want to look and feel your best?Even if you've spent much of your adult life glued to your couch, it's never too late to take steps to improve your health and fitness.April Treible of Lehighton wasn't exactly a couch potato, but setting a new goal for herself at the age of 39 spurred her to take some positive steps toward a healthier lifestyle."I wanted to join the Army," says Treible, following in the steps of her two sons and her daughter, all of whom are currently serving in the armed forces.While Treible was older than the permissible age to begin a career in the military, being a nurse gave her the opening she needed."They'll take 'old people' in the medical, legal and clergy (fields)."What was holding her back, however, was her weight. She needed to lose 20 pounds.Treible began running. After six months, she'd lost 40 pounds. And while she's gained 10 of it back, she's maintained the 30-pound weight loss.There were still hoops to jump through because of her age, she says, but on Nov. 14, Treible was commissioned as a first lieutenant in the Army Reserves."I worked in home care," says Treible of her previous nursing career. "I've seen the result of a sedentary lifestyle. You're more at risk for heart disease, diabetes, stroke. I know I wanted to avoid these things as I got older. Wanting to join the Army gave me that goal to reach - kind of like the carrot at the end of the stick."Even if you don't have such lofty goals like Treible, good health and fitness is still attainable, even as you age.Overcoming challenges"The biggest challenge middle-aged adults face is budgeting the time required to exercise and to prepare or buy the right food," says Dr. Mark Adickes, chief of the division of sports medicine and associate professor of orthopedic surgery at Baylor College of Medicine.Adickes says there are three important factors in maintaining health in middle age:• Cardiovascular fitness: running, biking, swimming and rowing• Muscle strength: weight training, barre workouts and Pilates• Flexibility: yoga and PilatesAdickes says the time you dedicate to exercise "must be etched in stone.""Once a habit has been formed, it is not difficult to maintain," he says.Treible is proof of that."When I started, I couldn't do one pushup or one situp. I couldn't run for a minute straight, let alone a mile."Today, she can do two minutes of pushups, two minutes of situps, and she's running 5Ks and half-marathons. In November, Treible will be running her first full marathon, the Marine Corps Marathon in Washington, D.C.If you're not up for a marathon now, or maybe ever, there is still plenty you can do.Adickes suggests deciding on a reasonable workout that can be done in an hour and seeking out professional help designing and performing an exercise regimen if needed.Treible says for Christmas in 2015, her husband paid for sessions with a trainer. In addition to working out with him, the trainer told her about different fitness apps to help her achieve her goal, such as "Couch to 5K" and "My Fitness Pal." Then he made her send him screenshots of her protein, carbohydrate and fat intake, which is just as important as exercise."Input, or nutrition, is actually just as important as output, or exercise," Adickes says. "Nutrition needs to be a lifestyle choice, so find a healthy eating pattern that works for you. Make your diet something that can be sustained, and allow for a cheat meal once a week."Adickes says stick to lean protein, vegetables and fruit. Avoid sugar and consume alcohol in moderation. He also recommends a daily weigh-in."You are going to mess up - get back on the horse when you fall off."Treible disagrees - at least for now.She's having a "No weigh - No way" summer."If you weigh yourself every day, you get disappointed," she says. "It's my way of taking the pressure off myself. It's how you feel, not how much you weigh. I met my requirements for the Army. There's no reason to put so much pressure on myself."Treible says she's also not one to be so open about her private life, but as she moved toward her ultimate goal, she realized her success was inspiring others."It's not in my nature to share things like this, it's out of my comfort zone. But then my friends found it inspirational and started doing things themselves to improve their health," says Treible. "Even if you don't like to run, just find something."Get up and move."