I am a healthy 8.5 stone 5'5'. I enjoy going to gym and like the feeling after going. At the moment I do an hour at the gym saturday, wednesday and sunday. Plus half an hour Monday and Tuesday. I am not trying to lose weight. Is that too much? I just go on the treadmill and cross trainer most of the time.
How often do you go?
Frankly, unless the gym has a swimming pool and you have no intention of resistance, gymnastics, strength training I wouldn't be using the gym full stop. Pair of fitted trainers and a heart-rate monitor do me fine to go running outdoors and enjoy it.
In answer to your question, these days I do 2 days in the gym (40 mins~) and 3 days out (running, climbing) pw.
That sounds like a reasonable amount - as long as you're eating and resting enough so that you recover for each session then it's not a problem. To be honest, I think that you'd be better mixing up your routine a bit, as this is going to add interest but also improve your fitness overall. Add in some time on the rowing machine and vary the sessions that you do between longer, steady sessions and sets of shorter, faster intervals. Also, I'd recommend adding some weight training - maybe a simple full-body routine twice a week.
The amount of time I spend in the gym varies depending on how much exercise I do outside of the gym, but over the summer I was probably doing about an hour a day 6 days a week. As long as you're eating enough and giving yourself enough time between activities which you take longer to recover from, like weights sessions, it's not a problem.