|What's your fitness age?|
Let's start with VO2: this is the volume of oxygen your body will use in one minute. It's the ratio between the amount of oxygen in the air you inhale divided by the amount of oxygen in the air you exhale, all during the course of one minute.
To save you the thousands of dollars it would cost to measure this with specialized equipment, some fantastic sport scientists have developed some simple formulas that you can use to calculate this and give you some useful numbers. A couple of them can be found here.
Once you have your VO2 Max number, you can compare it to a chart that looks at age and score. Here's a link to charts for both men and women. Men between ages 25-55 should have a VO2 Max between 32-42, and women should have scores between 28-38
To get a better sense on where you are fitness wise and calculate your 'fitness age', you can use this fitness age calculator. You will need to also know your waist size (the measure around your belly button, not your hips) and resting heart rate (measure this after having been settled for about five minutes).
If you are having trouble calculating, then just comment on this page and I will help you out!