Ivory Netsuke

My Dad bought this ivory netsuke at an auction and has collected a few others over the years (a turtle, a dragon, two monkies, a dog and a warrior) Another thing is that its made from one block of ivory and that's pretty impressive, taking into account that it stands at about the same height as my little finger and that i have pretty small hands. Id really like to know just how old it is, if someone could provide that information here, id be pretty grateful.