I'll second Tojo. At the end of the day, it takes as long as it takes. last year i only completed 4 builds. This year i would like to build more, but i am not going to knock myself out over it or risk lowering the quality. Some days even though i decide what i wnat to achieve that day, i don't touch a model.
Some people can build more than one at a time. Personally, i find it confuseing. I gave up on it a long time ago. Then last month i thought i would try it again just for a couple of builds. I even decided to set certain days for one build and other days for the other one. But that didn't work. I just ended up concentrating on what i classed the priority. To be honest, i don't think you save that much timed when it comes to painting.
I'm in my early 40's and got a stash of over 200. I will be very lucky to build all those, and i still add to it, but not as much as i used to. But what the hell. I can always take them with me.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3