There is no medicine or exercise to get rid of glasses and from  this age ,it's likely to progress. You make up your mind to opt for the sevices where glasses are not a bar .

Improving general health and diet will definitely contribute to better eyesight however it cannot be said that if you eat two carrots a day then your power will come down by 0.50 or 1.0D. Still you must employ these measures. Also practise visual hygiene by reducing screen time, exercising outdoors for 1 to 2 hrs per day. Also read in good light, sit in proper posture while reading. Eye exercises are also good to relax the eyes and prevent eyestrain. Regarding joining air force do not make it a condition that you will be happy only if you can join the airforce. Look for other options as well. If after following the above mentioned measures the eyesight improves then you can apply for the Air force.