I am 27 and was in a relationship with a woman aged 25..
Resistance exercise (weight training) improves your heart health, though not as well as aerobic activity. But remember that any exercise is better than no exercise at all, so fit in 30 minutes every day or three times a week.
Be creative and find a few spare minutes throughout the day to get active.
health.howstuffworks.com; uihealthcare.com; kidshealth.org;