Re: metabolism question...
Truth be told a person's metabolism slows down gradually with age... a slowdown does not occur when you reach a specific age.
So much more than age effects one's metabolisim, general health, diet, medications, activity, etc. You can employ many strategies to fight this uphill battle - eat a healthy balanced diet, increase activity, and focus on maintaining the health of your vital organs (heart, liver, kidneys).
If you have experienced any sudden changes that are causing concern - such as suddent weight gain (or loss), changes in appetite, or changes in your digestive process, its likely not "age" causing the problem and warrants further attention.