Hi geek,
I don't think you should forget going to the gym just because of your age. My mum is at the gym 3-5 times a week at the age of 50+. She's very fit and I don't think that would be a problem for you (unless you have an unmentioned illness that would inhibit you going).
The most common reason for people not seeing any progress is lack of commitment or not having a routine. Routine is key in seeing gains/losses; you absolutely have to be consistent or you won't get anywhere. Also, don't expect immediate results, training your body will take time. There's also no reason why you wouldn't be able to increase your muscle mass too.
As for food, you'll want a variety of nutrients that are involved in the muscle development process. Some of the most important are magnesium (absolutely vital), potassium and amino acids (a complete profile). Your electrolytes (magnesium, etc) should ideally come from fresh vegetables, nuts and seeds, beans and legumes.
You will also want to take in liberal amounts of oil and water. Water is vital in cell metabolism and getting a good supply of oil is important because every cell membrane in your body is made from oil (EFA's). Your dietary intake of oil usually indicates the health of your cells. Your oil should be in the form of unsaturated (poly and mono) fats from oily fish (fresh), avocados, nuts and seeds and maybe an oil supplement if you want, though a supplement is generally not necessary as a diet including the above should supply you with your required amounts of fat.
You will want a diet rich in amino acids to rebuild your muscles after your weights routine. Nuts and seeds are an excellent and complete source of amino acids, as are avocados, beans and pulses. When looking to gain muscle mass you also want to space your meals out evenly over your day. Instead of 3 larger meals, eat 6 smaller meals with equal amounts of nutrition in each, especially amino acids. You should also have healthy snacks such as nuts and seeds in between, and don't forget to stay hydrated all day.
You may also want to take barley grass in powdered form as a supplement, as this is an extremely valuable source of protein and has a range of other benefits, which I will leave you to explore.
Try taking a look at this video:
http://www.youtube.com/watch?v=YdB2I...eature=related
Good luck,
George.