I am guessing late 1950s. The 26.4mm seat post diameter is consistent with plain gauge Columbus or 531 tubing. Don't worry about the stamped dropouts, which Capo continued to use into the early 1960s, although their top-of-the-line Sieger model got U-shaped braze-ons to improve the function of quick release axles and give the appearance of forged units. The lack of a derailleur hanger is also not necessarily a deal-killer, either, since "claws" were still very common in the late 1950s.