Cultivating Mindfulness is the best antidote we have to cope with the changes caused by inevitable aging in sexuality. Our minds and how we pay attention and the loving presence we bring to the sexual union is what truly matters in enlightened sex.
Taking good care of your body and avoiding illness secondary to poor life-style or stress helps maintains sexual health. Healthy desire is also a result of "secure attachment" you create with your significant other.
Good news: men are living longer and being sexually active well into their 7th decade. Bad news: life-style and general quality of health (heart health, obesity, hypertension, diabetes,etc) will dramatically affect sexual functioning.