How Old Was Timothy

How old was Timothy when this scripture was written? 1Timothy 4:12 Let no man despise thy youth; but be thou an example of the believers, in word, in conversation, in faith, in purity. It is falsely assumed that Timothy was in his late teens or early twenties when these verses were written, but a quick check of bible chronology, and the established dates of the writings of the following letters, give us a far better grasp of Timothies age through the scriptures.