And his rugby development took another massive step forward on Saturday when he replaced Freddie Burns with just over 20 minutes to go in a white hot West Country derby against Bath at the Rec.
It didn't faze the Exeter born player as he more than played his part as Gloucester earned a narrow win, kicking a 66th minute penalty to secure the points.
Some may feel unsettled by the frequent changes in scenery but the level headed Mills is taking it all his stride.
"It was nice to get the start for the U20s up in Scotland but then I was back in Gloucester as Freddie (Burns) was with the Saxons and Tim (Taylor) was injured.
"It's tricky sometimes because I'd like to do both. But you can't play on a Friday night for the U20s and then Gloucester at the weekend. I'd like to try but there are rules against it!"
When Freddie Burns went down with cramp due to the heavy going underfoot at the Rec on Saturday, there was a rapid call to action but Mills believes that his sudden entry into the melee actually helped him.
"I really didn't have a clue. I was just doing some warm up exercises when the call came across the radio to get me on. I ran back to the bench and I was literally straight on without any time to think about it.
"It was good in a way because I was straight into the action and there was no time to over think things and let nerves or emotion get in the way.
"You've got Rory Lawson inside you and Eliota Fuimaono-Sapolu and Mike Tindall outside you. Those guys possess so much experience that they make life as easy as possible."
And, of course, his big moment came when Matt Banahan was penalized for not rolling away and Wayne Barnes awarded a penalty.
With the TV cameras zooming in on him and the match potentially on the line, what went through his mind?
"I just thought 'put it through the posts!' When the pitch is like that, anything can happen when you're kicking. Your non kicking foot can slip or you can get a bad contact.
"The ball was sandy and muddy and tricky to kick. You could see that from some of the kicks that went before. It wasn't ideal so I was just happy when I looked up and saw the ball going through the posts.
"I'm just making the most of the experience. Even sitting on the match, you're experiencing the atmosphere and it fazes you less and less the more you're involved."