How Old Am I, Really? These Tests Measured My Biological Age

How old am I, really? I spat in a tube, swabbed the inside of my cheek and pricked my finger to find out. 

I mailed my samples to three companies that promised to tell me my “biological age” based on chemical modifications of my DNA. The results, the companies said, would be based not on when I was born, but on how much my cells and organs had aged.