Is this a little early for that kind of weather in Golden?
Nope. I have personally been snowed on as early as mid-September in the Foothills, and in some years the snowcaps on the mountains stick around through June or July.
There is a consistent problem with newbie folks who come out here and decide to run around the mountains in warm weather in shorts and tee-shirts and the like and then get caught in a sudden snowstorm. Every year there's a couple of news stories about this, sometimes involving fatalities.
It used to be that there were a number of small planes which had been missing for decades up there in the high country because their little Continental engines were trying to claw their way over the peaks, but I guess modern technology like satellite imaging and "stuff" has located most of them by now. Ratings of 150 horsepower at sea level do not equate to 150 horsepower at 12000 feet and sea level climb rates do not pertain, either. (IANAP) ("I am not a pilot.") I guess the mountains resent those buzzy little annoying planes and tend to take swats at them.
Possibly, by observation over fifty years of living up here, the most "outdoorsey" deaths seem to involve rock climbing and skiing. Oh, and avalanches, which usually involve cross-country skiing anyhow.
Note the snowfall amounts throughout the year in the tables in the link below, and this remark: "Again, with altitude being such a large factor, snow in the foothills can start as early as the first week of September and extend to the last week of June, especially at levels above 7500 feet."
http://www.skyviewweather.com/climatology/