The info on diving is piffle.
Unless warned off exercise (they don't do that) there is no reason not to dive - it's good exercise and does not stress the joints - normal drift dives are not going to raise the heart rate (fighting a current can).
The depth one dives to causes no particular additional stresses on the body - max depth on air is around 130ft for 3 minutes for a no decompression dive - nitrogen is forced into the tissues - it causes go issues but if one ascends too quickly instead of releasing slowly it releases in one go - like opening a shaken fizzy drink and evolves bubbles - these bubbles for in joints etc causing the pain associated with the bends. The point is depth is not what does it but time under water - a 40 minute dive at 50ft forcing in as much as a couple of minutes at 130. Just as with flying one must plan - modern dive computers have educed significantly the chance of a miscalculation.
If you've been told exercise is ok irrespective of age diving can be part of it - just make sure those you're diving with know not to ry battling any 20kt currents!