blimey 10 stone that is slim...Your never to old to start training best thing for you to do is make sure your food is in order.I think what you need to do is eat as much carbs as you can jacket potatos past rice eggs and get a good quality protein shake too and have them a couple of times a day between meals.Genly ease yourself back to the gym but remember muscle has memory and will soon come back just take it easy for the first few sessions and dont go to mad.You will soon put on weight try sticking to sets or 8 or 10 no more