Well, some of these have answers, even if they might require a little bit of waffling.
There are four main ingredients in beer. Here’s where they come from and how long it takes…
Water requires little or no processing before use. There may be some filtering or chemical additives to adjust pH levels and such, but these take virtually no time.
Malt requires that the barley be reaped, dried, and malted, a process that could be done at home in a couple of weeks at the most. The malting is a combination of soaking and roasting.
Hops need to be harvested and dried. In drying my own hops, I’ve been able to put the hops into the brew within about a week of when I took them off of the plant.
Yeast is usually kept in an active culture, ready to use. If not, it’s a day or two to get a good culture going.
Once the four ingredients are ready to go, you have a brewing process followed by fermentation. The brewing is quick (an hour or two). The fermentation can be as short as a couple of weeks for an ale or as long as a few months for a lager, or even a year for a barleywine.
When fermentation is complete, it just needs to be bottled and refrigerated and you’re ready to go.
With no bottlenecks in the process, you could be drinking a glass of ale within about a month of when the grain was waving in the wind.
More likely, you’re drinking a commercial lager, which has shipping times and shelf times added on, and it could be many months.