This is a wonderful question, and for someone not taking in animal products, a really important one.
In general, men in earlier life, (up to age 65-70 or so) tend to have lower incidences of osteoporosis, mainly due to having larger skeletons and no rapid hormonal changes as are experienced by women.
Bone is living material, and is constantly changing. Old bone being removed, and new bone being created. In youth, more bone is being created so the skeleton grows larger and stronger. In older age, the amount of bone tends to decline as the removal phase is more prominent than the creation phase.
So, as for calcium, the important part is to get adequate calcium into the system for greater bone health and for overall health.
The best foods for bones are plant foods. One of the greatest sources for calcium in the diet is green vegetables. The best part about getting one's calcium from vegetables is that they have a higher absorption rate than do dairy products. Also, the retention rate of calcium in the system from veggies is higher than that of animal products.
Supplementing with calcium is an individual thing, but the place to start is with food sources, rather than supplementation. The standard recommendations for supplementation are based in part on the attempt to try to offset the negative effects of the Standard American Diet.
As for calcium in plant foods, 2 cups of collard greens can give you 600 mg of calcium, two cups of spinach can give you 500mg of calcium, and 2 cups of kale can give you approximately 350 mg of calcium. A healthy vegan diet can give you plenty of calcium. If you want to shoot for the RDA for calcium, you can keep your eye on about 1000 mg per day. Look to get that from the diet though. The other critical piece in bone health is weight bearing exercise. Weight bearing exercise builds bone and muscle, and is crucial to balance in later life.
With exercise and a whole foods, plant based diet, stronger bones can be in your future.