>I would guess at least 20 years.

You needn't type any further than "I would guess" because the type of can I was referring to are what you call "the new design"; the "old design" dates from the 1960s-early 1980s

The tubular part is thickest near the top and thinnest at the mid-point between the two. This has been accomplished by rolling the aluminum sheets in two directions diagonally before pressing the can out of the sheet. The top is rolled on separately after the can is filled with product.

If you put your foot carefully on the top of an empty can --you must load the perimeter of the top uniformly and at the same time-- it will support your weight until some part of the tube is deformed (have someone tap the side of the can with a stick), at which point it will collapse almost instantly. I used to do this frequently about 10-15 years ago, and at the time I weighed 245 lbs.