Hello Bridget, welcome to WAGS. :)
Well, I wouldn't swear to it, but the A might mean aluminum. Is it aluminum? See if a magnet sticks to it. If it does stick to it that means it is cast iron rather than aluminum. As for age, according to the Book of Griswold and Wagner by Smith and Wafford, the number 7 griddle, pattern number 744 was made circa 1925 to 1950, so yours being a 745 number, that should fit right in there as well. Thats my take on it anyway.
Again, thanks for stopping in, don't be a stranger, come back and check us out.