Yes, it gets to terminal velocity pretty quickly, it's decelerating for most of the fall as the atmosphere gets denser.

Estimated kinematics from a prior flight. https://flightclub.io/result/2d?code=SN91

edit: To clarify, a drop from 100km would not hit terminal velocity quickly, it would accelerate until it got to the thicker lower atmosphere where it would be rapidly slowed.

Hitting a speed and sustaining it throughout the entire re-entry are two different tests?

Terminal velocity is defined as the velocity at which the force of gravity is equal and opposite the drag exerted by the atmosphere. So, yes, I think Starship is hitting terminal velocity at 10 km, but the velocity is smaller than the terminal velocity at 100 km. Less atmospheric drag at 100 km means the velocity is greater than at 10 km, so 100 km flight would be different than a 10 km flight.

I don't think coming up to terminal velocity in atmosphere is really the concern. What's more interesting is getting up out of atmosphere, falling back down at a speed that's many times higher than terminal velocity, slamming into atmosphere at that speed, and then dealing with the reentry heating and other forces that result from that.