A native of County Galway, this is his first year playing for the Connacht Academy after finishing his secondary education at Cistercian College Roscrea, County Tipperary.
When asked about the step up from schools rugby to training as part of a professional academy, O'Brien shows his thoughtful nature, "We spent a lot of our time in Roscrea focused on rugby but it is different in the sense that it is a lot more professional. As my lifestyle was always built around rugby it hasn't been that much of a change as you might expect."
A feature of the current Connacht academy set up is that the academy players train alongside the senior team. This is something that the young player relishes, "it is brilliant. It shows you that you are within touching distance and that you are not that far off, when you are training with them you are able to know that you are part of the team."
He adds: "It is good as it drives you on to be ambitious. You can also learn off the lads, which is just brilliant."
Yet he shows his grounded nature when talking about the distance players at Under 20's level have to go to play in the senior RBS 6 Nations, "I suppose we are not too far off it but at the same time there is also a very long way to go.
"There are a lot of people who play Under 20's but don't go any further. It is good to see that we are getting closer and it just gives you more of an impetus to keep going and give it absolutely the best shot that you can and see if it works out."
O'Brien's rugby journey began at a very early age, "I have played for Galwegians since I was a baby! I started there when I was five or six. My family have been a big Galwegians family for a long time, so I suppose I was always going to end up playing rugby."
He speaks with great pride of his late father Ian's involvement in his development as a young player, "my dad always coached me. He coached me up until under 17's. He would have been my driving force in terms of guiding me with my rugby. He was a very good coach and he thought me a lot about the game. I put most of my success so far down to him."
As well as pursuing a rugby career, the forward is studying civil law at the National University of Ireland, Galway (NUIG). Carving a path separate to sport is something he highly values, "It is essential in my books to have the studies. It gives you a distraction away from rugby, if I didn't have my course in my life, I would just have rugby and that is not healthy.
"I think you do need to have a degree behind you in case the rugby does not work out. When you are training every day, it is nice to take a break from that and go to college and do your work there."
However, there can sometimes be difficulties in co-ordinating a full time training schedule with academics but O'Brien has found support from the Irish Rugby Union Players' Association (IRUPA), "it is tough enough to balance the rugby and the studying. However, there has been a lot of help from IRUPA, in helping us to balance the two lifestyles I have found them very helpful.
"Whenever I have a problem with college, for example, if I have missed an assignment because I have been off playing a game in a different country, IRUPA could give me a hand in maybe getting me a small bit of leeway in terms of the deadline. Overall, if I ever have any problem, I can just go to them with it."
O'Brien recently had an encounter with his famous namesake that left the Leinster, Ireland and British & Irish Lions back row star a little surprised, "He had to present the jerseys for the Welsh match and he got a bit of a shock halfway through when his name was called out when he had to present my jersey to me!"
Having a senior international visit the Under 20's camp, "blends into your match preparation, it gets another buzz going for you."
Playing for his country at Under 20's level is something that O'Brien enjoys for several reasons. Firstly there is the step up in standard compared to other age grade levels, "You have to play at a high standard to improve. The better the standard you are playing at the better the player you become. So, definitely it benefits you as a player."
Then there is the sense of achievement that go beyond the personal, "It just makes you proud to represent your country. It is great representing your family and friends and knowing that they are proud. It is an unbelievable feeling to go out wearing the green jersey and I am always so proud running out onto the pitch in it."
Sean O'Brien is certainly a name to keep an eye out for in the future.