He looks so young. Please don't let me fund out he built Build while I was ogling the stripper sprites in Duke Nukem and barely managing my CGSE maths homework...
> 08/24/1993: Ken signs employment agreement with Apogee Software Productions. A special provision on the contract says that Apogee cannot interfere with Ken's education.
Inferring from the first entry in the timeline, he must have been 17 or 18 then.