You are past the age when you should not be working out with weights. It is suggested that when the skeletal system is still in developmental stage, it is better not to use anything but your own body to train. But that does not apply to you now. So, you can safely train at a gym now. It would be advisable, however, to work under a trained instructor so that the risk of injury is low.
The advantages of working out in a gym are many: seasonal changes do not hamper your workout, the factors that you encounter in a gym are constant and you can motivate yourself to work out in a crowd on the days that you are feeling down.
The disadvantages are that the same conditions can work to be deterrents: the monotony of going to the same place every day as opposed to working out in the natural environment, the crowds can get too overbearing and if not ventilated properly, the gym environment can be detrimental to fresh breathing!
All in all, you have to assess what suits you and go for it. Try it out and the best way to shake off monotony is to have variations in your workout.