Well, when you say you're going to "grow into it"...can I ask how old you are? At 5'10" 170, a 158 would be fine for you. If you're gonna grow another few inches a 160 would be a good bet too.
In reality though, you're not going to feel much difference between a 158 or a 160.
I'm about the same specs and have rode boards all the way down to 153 and as high as 159. IMO, I would go shorter if you just plan on cruising and groomers. It will allow you to maneuver the board easier. Longer boards are good for higher speed and stability.