If you're training for boxing, intensity is more important than volume in regards to conditioning work. You can make the same if not better adaptations to high-intensity training compared with traditional steady state endurance training, but with a much lower time commitment.
In the same position as you in terms of age and fitness. Started training again today myself. It's good to do a mixture of distance and high intensity running but the latter is more effective for boxing. Can do it on a treadmill using time intervals. Or if you don't have access to one, you can do some Fartlek training. Find yourself a football pitch jog the length and sprint the width by the goals. If not sprint to one lamppost jog to next and repeat. As mentioned above it really doesn't take long training this way until you're gone. Much more effective than an hour long jog.
Or If there's steep hills by you do hill sprints. Great for stamina. If you want do some body weight exercises in between sprints.
I would try interval training: Run as fast as you can over a three minute interval, then walk for one minute to "rest". Then repeat 3 times. Good, intense workout in only 15 minutes.
I should have said run as FAR as you can in 3 minutes. The Evander Holyfield three minute drills are a good way to improve your cardio too. But they are tough.