16 miles x 3 days a week is a great start.
If your schedule allows you the time to add more miles or another day I say go for it.
A good way to ease into it may be to choose routes that allow you to do another loop somewhere in the middle so that on the days that you aren't feeling like extra miles you can just skip the extra loop and stick to your usual miles.
As opposed to there and back routes that are more of a commitment.
Enjoy!