It seems incredibly unlikely that you are too heavy for that bike. The alloys have nothing to do with flat tires. What's causing the flats? If there are two small holes near each other, this is commonly called a snakebite flat, and is caused by insufficient tire pressure for your weight and the terrain you've ridden over. I am a similar weight and height, and on 700x23mm tires I typically run 90/120PSI (front, rear) and I don't think I've ever pinch flatted at those pressures, despite hitting some minor pot holes etc at speed. Try increasing your tire pressure and/or running wider tires.

If it's just caused by punctures from road debris: A) avoid as much as possible: B) buy tires with better flat protection. The schwalbe marathon line is well regarded, as are conti gatorskins, though I've personally never run either. I find where I ride that road debris doesn't cause so many flats that I need especially resistant tires.

Also, it is bogus to replace tubes every time you get a flat. Spend a few bucks and get a flat kit. If you've done all that work on your bike, you can figure it out. Seriously patched tubes are good as new.

Other things to check would be any burrs in the rim, or badly applied rim tape.

Sweet looking bike, nice score.