I also expect your mechanic used a commercial "chain checker" which, as dabac noted, tend to give erroneously high wear reading.

Using my experience as a data point, I'm relatively light at 150 and older at 74 but I ride a lot and, as my forum name suggests, climb a lot. I get 6000 to 7000 miles on a chain before it measures over 1/16" elongation over 12" (24 pins). I do keep the chain relatively clean and relube it at 300 to 500 mile intervals and immediately after getting caught in the rain. So, unless you are heavy, ride a lot more than you said or are completely negligent of chain care, your chain should still be in good shape.