In order to become a good leader, you must first become a good follower. This means supporting your Captain and being respectful while being pro-active in the decision making process. If this means that sometimes you have to bite your lip, then so be it, that is the essence of good character.
If you don't develop the traits of a good follower, you will never develop the traits of good leadership. I imagine that the F/O in question will enjoy a long career in the right seat.
In the scenario described, with the benefit of hindsight and the other posts, I think the correct actions would have been;
1. Take control yourself. The comment; "I'm flying the aircraft" indicates a break down in CRM. We are flying the aircraft you as PF and me as PM is more accurate. BOTH pilots must be happy with state of the aircraft at all times.
2. On the ground, conduct a thorough debrief. Make him understand the above.
3. Tell him that he is flying the next sector (Weather permitting). Thoroughly brief him on your expectations of his descent profile. Give him gates to pass; e.g. 250 kts/ 5000ft/ 20 miles and 210kts/ 3000ft/ 12 miles and Flap 5/ 10 miles.