Solely being old isn't the problem. The early variants of 737s were solid. It became a problem with later versions with bigger engines etc: you can probably get away with some minor CHANGES without overhaul the design as long as it's still within the threshold of the original design, but those MAX variants crossed the line. Thus MACS was introduced. MACS, to some extent, was a feasible workaround if Boeing did not cut the corners by outsourcing the implementation and chose to only have one critical attack angle sensor. But if things only stop there, those two disasters could still have been avoided if the pilots were aware of the existence of MACS. But again, Boeing decided there was no need for the pilots to know it at all.
After the first crashed MAX's FDR data release, I was wondering if there were something massing with the pilots but I wasn't sure. Then the 2nd crash happened and the FDR data looked almost exactly the same, I was almost certain there was some undisclosed mechanism causing nose diving. But as we all knew, Boeing denied such thing until later.
You can see that in the whole Boeing had been SUPER CONFIDENT for sure, and thus I now have no confidence in it at all.