Boy, takes one back.. I think the earliest was helping Dad build a 20 mule team borax wagon set that you could get with box tops. Helped Mom with a one of the Knight in armor kit. Don't remember which was my first model I built myself, probably the USS Olympia, in 6th grade. First car I remember was in 61 when I built an AMT 32 pickup which I chopped the top on using a hacksaw and gluing thread to the distributor for plug wires, inspire I expect by an article in Model Car Science. And all us boys of an age got Big Ts for Christmas the first year they were available. Alas all gone except the memories and magazines.