How old is it when a baby starts to hold a toy?

4-6 months. Really, grasping should occur by 4-6 months, with transfering toys, rattles, etc from hand-to-hand by 6 months or so. Babies at 4 months generally should be purposefully reaching for things with both hands by about 4 months with good, solid grasps at that age.
Within 12 months. http://www.healthychildren.org/english/ages-stages/baby/pages/developmental-milestones-12-months.aspx?nfstatus=401&nftoken=00000000-0000-0000-0000-000000000000&nfstatusdescription=error%3a+no+local+token.