Much of the decline in metabolism is due to loss of muscle-mass. This can be counteracted with weight-training, of course.
Surely, eating to keep your metabolic rate high in the first place would prevent this issue. The problem is that the vast majority of people have no idea how to eat correctly. And most simply do not care. Their diets are full of PUFA, low protein and processed junk. Their whole mentality is based around eating less. Their muscles dissapear, and some will deteriorate and blow up like balloons as their bodies go into a state of crisis, running on stress hormones. So what do they do as they gain weight? They eat less. Causing more stress, and increasing the ability of their body to cling on to fat at whatever cost. Their body is on the decline, and as they get older, it's only going to get worse (especially considering they don't have a clue how they got themselves into the situation, or how to get themselves out of it).
OP, people don't just 'eat less' as they get older. An increased metabolism actually increases appetite, considerably. It's something I've witnessed with myself over the past 6 months. The more my metabolism increases, the hungrier I get. My body needs feeding and it craves nutrients. Calories + nutrients = less stress on the body. Which then breeds an environment in the body for favourable things to happen (an increased anabolic state, for one).
People will get less hungry as they get older as their metabolism drops. But one affects the other. If you let your metabolism drop in the first place, you're hardly giving yourself a chance. It's almost as if you are handing your body the keys to the ageing process. Defeat.
I would consider weight/resistance training to be a healthy form of exercise, if done correctly. Especially if you compare it to long distance running (there's a reason it is painful to your body. It's bad for you).
Edited by Thorsten2, 21 April 2014 - 10:19 PM.