My father brought home a Brother (I forget the actual model number) in the early 1970s. I can't remember the brand or model of the first one I owned, thanks to my parents, but I can picture it even now. It was the typical LED-display calculator of the time, four functions plus constant. I remember the nice large square keys compared to some other models, with red and orange for the C and K keys.
Like many others, it was probably sold under several different brand names. I think I was about 8 or 9 at the time, so that would place it to 1974/75. Then my parents bought me a Texas Instrument Programmable TI-57 for Christmas in 1977.
Despite that, and perhaps aided by having a mother who was a math teacher, I still learned to do mental arithmetic in my head, and unlike many of today's kids, don't end up using a calcultor to add 2 and 2!
For some great old machines, including some of those earlier models from the 1960s, have a look here: http://www.oldcalculatormuseum.com/
If you're like me, and then discovered just how wonderful the Hewlett-Packard models were, have a look at this site: http://www.hpmuseum.org/