In his first season with U17 US National Team Development Program back in 2010-11, he helped lead his country to a gold medal at the Four Nations Cup, captured second with the USA at the 2011 World Hockey Challenge and capped off his year with a first-place finish at the 2011 Vlad Dzurilla U18 tournament in Slovakia.
He suited up for the U18 US National Team Development Program in 2011-12 and continued to build on his already-impressive resume. The NTDP squad won gold at the 2012 U18 World Junior Championship. He was also invited to the NHL Draft Combine in Toronto and was ranked 31st amongst North American skaters in Central Scouting's final rankings.
While he had committed to play for Miami when his time with the NTDP was done, he opted to go the OHL route this season after his rights were dealt to the Windsor Spitfires. The choice, he felt, would offer him a quicker route to the professional ranks and would place him on a team that would contend for championships; he would be, theoretically, continuing on with his winning ways.
That did not happen in the 2012-13 campaign.
The Windsor Spitfires are on the outside looking in at the OHL postseason after finishing ninth in the Western Conference with a 26-33-9 record. The team hovered at the .500 mark for the majority of the season and struggled to find offence. The Spits ended finishing the year with 212 goals scored - second last in the Conference, trailing the Erie Otters who finished in last place.
The worst part for Sieloff? He was sitting on the sidelines when his team was eliminated from the playoffs. A groin injury kept the rearguard from playing since Feb. 15 and limited him to 45 games in his season with the league.
"It was tough," the 18 year-old told CalgaryFlames.com. "You want to be out there, trying to help your team win."
Dealing with his injury was an exercise in patience for the Ann Arbor, MI product but much like the season as a whole, it was a learning experience for him. The issue popped up late in January during a game. It progressed throughout the night and by the end of the contest, he thought he may have pulled his groin.
A battery of tests were run and it turned out it wasn't a simple pull. He headed west, having the Flames medical staff take a look at the malady and give him a diagnosis. He went through the process, got a handle on the problem and started to rehab his groin in Calgary.
When Sieloff hopped on a plane back to Windsor, he felt he would be able to get back into games soon. He suited up on Feb. 15 but it became evident during the outing that the injury hadn't progressed the way it should have. He sat out for another couple of weeks before he was officially shut down for the season.
"Of course I wanted to play but, at the same time, I realized that I wouldn't be much help to the team if I wasn't healthy," he said with a sigh. "It's the kind of thing that takes time to heal and recover from."
Watching his team struggle throughout the season was obviously a frustrating experience for the defenceman but when he took a step back and looked at the situation, he saw it in a different light. Rather than letting that frustration take over and cast a dark cloud on his first year in the league, he is looking at the 2012-13 campaign as a learning experience and a building block in his career.
"We dealt with a lot of adversity this year," he said. "We had a lot of injuries this year - I think we had four or five season-ending injuries ... it seemed like every week, another guy was down.
"But that isn't an excuse we can fall back on. When we do get injuries next year, because they're bound to happen, you have to play through that - play through the adversity. Different guys have to step up in those situations and challenge ourselves to be better."
One bright spot for Sieloff was the 2013 World Junior Championships in Ufa, Russia. He wasn't expected to even make it out of the Hockey USA camp in Lake Placid last December but his tenacity, determination and gritty style of play kept him on the roster that would play in the pre-tournament games.
Team USA chose to hang on to one extra defenceman until the final day their roster had to be submitted (which was delayed due to a medical issue) - which meant Sieloff and Matt Grzelcyk made the trip to Ufa without knowing if they would actually be a member of the team when the tournament started.
Sieloff's hard-nosed, shutdown style won out over Grzelcyk's two-way play and the defenceman went on to capture another gold at an international tournament as the USA topped Sweden 3-1 in the championship game.
"It was just an incredible experience," Sieloff said of his time in Ufa. "It was a hard road to get there. I didn't know if I was going to make the team or not but I stuck with it, kept working for it and played my game, my role ... everyone had a certain role on the team and I think that's why we were so successful.
"I definitely think it was a step forward in my development."