I know you might not like the answer to this but
sleep at least 8 hours at night (the same way you focus on your programming you should focus on sleeping),
have proper diet and
exercise at least one hour a day (weight lifting, cycling, running, swimming, a mix of these or others or whatever you like) as long as you remain active (your heart's beating and you're sweating) that's what's important. As with everything in life:
do NOT over do it. (Excessive idleness or activity is both detrimental.)
Obviously, as you age, your skin will naturally start to sag and there's really no sure way to fix that naturally. You'd have to resort to plastic surgery.