We just bought it and have no idea how old it is

Is it the original engine? What brand engine is it? For example if it is a Briggs the code from the model number block, it has the model, type, and (date)code. The first two digits of the code are for the year, the next two for the month, the next two for the day, and there are a few other characters, but not important in determining the date of manufacture. Next example is a Tecumseh engine. Look on the model/serial number tag, find the DOM, date of manufacture. If it is a four digit, first is the last number of the year, and the last three are the day of the year. The problem with that method is that the DOM number reoccurs every ten years. Then you have to guess which decade it was made in. Tecumseh fixed this in 2004 with a five digit DOM code with the first two numbers for the last two digits of the year. Anyway, let me know what you have.