I learned to SCUBA dive from a Navy Dive Master back in the late 1960’s. Yes, I learned on a two hose Aqua Lung regulator and yes, I owned a set of twin steel 72 cu ft tanks (AKA Sea Hunt, Mike Nelson). The general rule for twin 72’s back in the day was that as long as you didn't go much below 62 feet you could stay there until you ran out of air in both tanks and surface without stops. Most people I dove with had a single tank reserve switch.
If you dived deeper, generally limited to under 100 feet, you used air much more quickly. If you stayed mostly under 60 feet, did a quick dive to less than 100 feet and didn't linger for more than a brief moment, decompression stops were not generally required although most of us did a stop at between 25 and 30 feet just to make sure that there was nothing on the surface of the water where we were planning to come up.
I know that the modern, lighter tanks have higher pressures and regulator gear has changed a lot, but but there are lots of arm mounted dive computers on depth/decompression.
Please see 26, for your thoughts.
I also learned on steel twin 72s with two-hose regulator, in BUD/S in 1979.