My child is 19 months and still puts lots of things in her mouth, but I did find that once she started walking it did gradually get less. This coincided with manual dexterity improving to the point where she could push buttons, open and close things, etc, which obviously widened her means of exploration.
But even though she is puttings less in her mouth nowadays, if anything I have to be more vigilant now about what she puts in her mouth, because she can reach more things, put them to her mouth very quickly, and also move out of my sight more quickly!