How much and what type of exercise to stay healthy?

Interesting question. I'm in a similar position. Not interested in marathons, triathlons, tough mudder challenges etc. Just want to maintain a level of fitness with a body that reflects it.

But all I can think of at the moment is that to look like an athlete, you have to train like an athlete.

Whenever I say something like "I was training yesterday" when asked what I've been up to, they always ask "training for what". Not sure what a good answer is. I did see one YT video where the guy said he was training for the day when someone might try to harm his loved ones, which is a good response, although I'm not sure how doing a **** load of pull ups will help in that kind of situation. Of course, the answer, "Training for the zombie apocalypse" sounds cool in the right circles but makes you sound like a weirdo in every other circle.

Which is a convoluted way of saying "BUMP".

Can we define "healthy average lifestyle" before i try to answer?

Here is the American College of Sports Medicine's 2011 recommendations:

The basic recommendations – categorized by cardiorespiratory exercise, resistance exercise, flexibility exercise and neuromotor exercise – are as follows:

Cardiorespiratory Exercise
Adults should get at least 150 minutes of moderate-intensity exercise per week.
Exercise recommendations can be met through 30-60 minutes of moderate-intensity exercise (five days per week) or 20-60 minutes of vigorous-intensity exercise (three days per week).
One continuous session and multiple shorter sessions (of at least 10 minutes) are both acceptable to accumulate desired amount of daily exercise.
Gradual progression of exercise time, frequency and intensity is recommended for best adherence and least injury risk.
People unable to meet these minimums can still benefit from some activity.

Resistance Exercise
Adults should train each major muscle group two or three days each week using a variety of exercises and equipment.
Very light or light intensity is best for older persons or previously sedentary adults starting exercise.
Two to four sets of each exercise will help adults improve strength and power.
For each exercise, 8-12 repetitions improve strength and power, 10-15 repetitions improve strength in middle-age and older persons starting exercise, and 15-20 repetitions improve muscular endurance.
Adults should wait at least 48 hours between resistance training sessions.

Flexibility Exercise
Adults should do flexibility exercises at least two or three days each week to improve range of motion.
Each stretch should be held for 10-30 seconds to the point of tightness or slight discomfort.
Repeat each stretch two to four times, accumulating 60 seconds per stretch.
Static, dynamic, ballistic and PNF stretches are all effective.
Flexibility exercise is most effective when the muscle is warm. Try light aerobic activity or a hot bath to warm the muscles before stretching.

Neuromotor Exercise
Neuromotor exercise (sometimes called “functional fitness training”) is recommended for two or three days per week.
Exercises should involve motor skills (balance, agility, coordination and gait), proprioceptive exercise training and multifaceted activities (tai ji and yoga) to improve physical function and prevent falls in older adults.
20-30 minutes per day is appropriate for neuromotor exercise.

http://journals.lww.com/acsm-msse/Fulltext/2011/07000/Quantity_and_Quality_of_Exercise_for_Developing.26.aspx

Once you have reached your ideal weight, if that was even your goal, I think to maintain status quo 30 minutes of cardio and 30 minutes of weight training 5 days a week is good enough. If your goals change to gain more muscle or lose more fat etc.,you have to adjust accordingly. Most studies essentially elude to this simple conclusion.