My Mothers' father, my Grandfather went out and bought both my cousin and I our own Lionel trains sets shortly after we were born and my father made a 4x8 layout that I had till I was about Six an then he started bring home Ulrich HO car kits from work, some guy would come around selling them and he a friend, Ray Abbott who had a younger sone Ray, would buy these kits for us and I would build a kit in the evening after school every time he would bring them home. Dad and Ray each built a Central Valley Side Door Caboose which I've always treasured as it was a Trussrod Under-frame and am running it in with my other
equipment, I still have all the the cars, most of them were from the '30's to the '50's though but that led to a small oval layout that was painted a light green with some trees on it for a couple of years but then at around age 8 I picked up a track plan book and found a plan I liked quite a bit and we built that and I ran the two Mantua kit locomotives I built on it for a number of years and had a lot of fun.
Then High School,I worked for about five years and back to College at night, the move to Coarsegold took place when I was 21 and when I was about 27 I again got the urge to unpack my old trains and I was off and running again. Buy then I had been opeating my own Photography business for awhile out of a 10x50' Mobile home I bought & lived in with little extra room for a layout but figured if I built a couple of extensions out from the wall, due to a window and drapes, I could attach a 4x8' sheet of plywood to them and fold the layout up against the wall when I wasn't running trains. That lasted for about Six months
and looking through some track planning books I again found a 4x8' layout I liked but was faced with the delima of where to put it so I expanded it to a 5'6"x9' layout or there about so I could build it to fit over the full size bed which I did and slept under it and had some fun with it but
got dismayed with the atlas track due to the lack of realism, from my stanpoint, and took all the track off, a big mistake as I did have anything to run, and started hand laying my own rail and a friend, Mark, who himself was an engineer for the SP and an excellent model railroader showed me how to build switches and believe it or not the first switch I built on my own was a three-way as I needed one, no sense picking an easy project, right?
A move took place in about 1975 up to my folks place as Dad & Mom needed my help and after a while the 5x9 monster was moved into one half of a double car garage and work again proceded on it. Well after some time and almost completely hand laying the exposed track I again became dismayed with the double track main I had planned, errounously thinking I need a double track main, without realizing it really didn't fit the time period I was modeling.
My father passed away in 1989 and some time passed but I again started doing more planning and came up with a a free-lanced 10'x10' track plan that I liked quite a bit with a single track mainline with passing sidings and built a portion of it as an around the wall layout.
Then 9-11 takes place and my thoughts change from RR to Defense of the country and my priorties change for about two years but I get back into working on the existing portion I had built which gave me some running ability up and down Ridgecrest Grade. After I got to looking the situation over I realized that if I dismanteled the old layout, which still took up the majority of the rest of that side of the garage, I would have a complete 10'x21' area to expand the new layout into and that is where I am at now and working on getting it going as I have several tables up but need to build several more to
complete the table work.
So I gues the short answer would have been from a very young age and have been involved
most of my life in the hobby.