When is it 'TIME'

As per title, when is it time to hang up the gloves. I am a keen kickboxer, I have dabbled in MT also. Over the past year I have been getting injured more and more. Usually rib injuries. I will be 40 in December. A year ago I would have laughed at the suggestion of giving up Kickboxing, recently though its as if my body has had enough. I appreciate this forum is full of people who are training hard to the best of their ability but has anybody ever hit this wall? I still love Kickboxing but I fear the writing is on the wall, the recovery time is getting longer and longer and it is tarnishing my enjoyment. I have tried Karate, trained as an art as opposed to a fighting method. It felt like a huge step backwards. I am not sure where to go from here. Dare I say lost. Any thoughts fellow mappers?