At 30 you're definitely not too late to start, I'm telling you. I saw at work how people in their 35-40s would come to the gym and do boxing - no problems at all. The main thing is to approach it sensibly and not jump straight into full contact. For a beginner at that age, boxing is probably safer. There's less strain on your knees and legs, everything is focused on your upper body and hand coordination. Kickboxing requires more leg mobility and good flexibility, and if you haven't done sports in a while, that could be uncomfortable.
Both have injury risks, but again - it all depends on what you're actually doing. If it's technique training and light sparring without hard shots to the head, the risk is minimal. I'd suggest starting with a trial month or two at both clubs if you can. Watch how people train, talk to the coaches - they should understand that you're a beginner and not expect you to go full contact right away.
From my own experience with cycling I'll say this: exercise at any age is better than no exercise. Start with technique, warm-ups, flexibility - and the boxing gloves and punches will come naturally. The main thing is don't rush and listen to your body, especially those first couple of months.