Tennis Europe
U12
Player
Netherlands
U12
Top 10
WTN
29.7
UTR
5+
Rankings updated on September 8, 2026
“My goals for the coming year are to reach a Tennis Europe final and to make it to the final of the Dutch U12 National Championships.”
Karsten Sietzema tennis player is a Dutch junior tennis player born in 2015 from Amsterdam who lives in Lelystad, Netherlands. Training at LTC Soestdijk with head coach Jeroen Rinkel and at the National Training Center in Amstelveen, he is a first-year U12 player, ranked No. 8 in the Netherlands and No. 2 among 2015-born players, has reached five national ranking finals this year and won four, and dreams of competing in a Grand Slam.
Through Tennis Papers, discover an exclusive profile and interview highlighting his tennis journey, playing style, competitive experience, and ambitions.
This profile is based on an exclusive interview conducted by Tennis Papers.
Karsten Sietzema · Biography, September 2026
| Full Name | Karsten Sietzema |
| Date of birth | May 9, 2015 |
| Nationality | 🇳🇱 Dutch |
| Residence | Lelystad, Netherlands |
| Age started tennis | 6 |
| Tennis age category | U12 |
| Netherlands tennis ranking | #8 |
| Tennis Europe ranking | |
| WTN rating | 29.7 |
| UTR tennis rating | 5.xx |
| Tennis club | LTC Soestdijk |
| Coaches | Jeroen Rinkel |
| Sponsors | |
| @karsten_tennis |
Karsten Sietzema · Interview, August 2026
What is your name, birthdate, nationality, residence?
My name is Karsten Sietzema. I am from the Netherlands. I was born in Amsterdam on May 9, 2015, and I currently live in Lelystad with my mum and dad.
What languages do you speak?
At the moment, I speak Dutch. I am learning English and I have also started learning Spanish.
At what age did you start playing tennis?
I started playing tennis when I was six years old. By coincidence, I joined a trial day at a local tennis club in Lelystad. From that very first moment, I fell in love with the game.
Are there other athletes in your family?
My family is quite fanatic about sports, although nobody has competed at a really high level in tennis. My father and uncle competed in sailing at an international level for several years, and my mother did some swimming when she was younger.
In which tennis clubs do you train?
I play tennis at two different clubs. I still play at the club in Lelystad where it all started. There, I play by myself, with friends, and I also train with my father. In Soest, at LTC Soestdijk, I have my training sessions with my coach Jeroen Rinkel. I also represent LTC Soestdijk in the national club competition.
Who are your coaches?
My head coach is Jeroen Rinkel, based in Soest. At the National Training Center in Amstelveen, my coaches are Ronald Wind and Jade Reijndorp. My dad also helps me a lot with my physical training, together with the physical trainers at the NTC.
What is your greatest strength as a player, and what do you need to improve?
I am really proud of my mental strength and my drive to get the most out of every training session and keep learning. At the same time, I am learning to accept that mistakes are part of the process and that I do not always have to be so hard on myself.
What is your age category and national ranking?
I am currently a first-year U12 player. I am ranked No. 8 in the Netherlands in the U12 national rankings and No. 2 among players born in 2015.
What have been your greatest successes so far?
My biggest successes so far have naturally been my most recent ones, as I feel that I am developing strongly as a player at the moment. Since the beginning of this year, I have reached five finals at national ranking tournaments and won four of them. Over the past year, I climbed from outside the Top 60 in the national U12 rankings to No. 8, and I reached the last 16 at the Dutch U12 National Championships. But those results are not what I am most proud of. What makes me really proud is the way I am developing as a player. I am becoming a player who can take control of matches and play an aggressive, dominant style of tennis, while becoming more consistent at the same time.
In which countries have you played tournaments?
The list of countries is still quite small, with the Netherlands and Belgium, but the plan is to expand that soon.
What equipment brands do you currently use, and are you sponsored by any of them?
I have been playing with Babolat rackets for several years now, and for the past few years I have been using the Pure Aero line. On court, you will usually recognize me by my The Indian Maharadja outfit and ASICS shoes. At the moment, we take care of all my equipment ourselves.
What is your next goal?
My goals for the coming year are to reach a Tennis Europe final and to make it to the final of the Dutch U12 National Championships.
What is your tennis dream?
My biggest dream is to have the opportunity to reach my full potential as a tennis player and, one day, compete in a Grand Slam.
Who is your favorite player and why?
It is really hard for me to choose just one favorite player because Carlos Alcaraz and Jannik Sinner are both right at the top of my list. But if I really had to choose, I would probably pick Sinner, maybe because the way I try to play myself is closest to his style of tennis. What I admire most about both of them is how they seem to play their best tennis when it matters most. Even with all the pressure they face, you can still see how much they enjoy competing and how much respect they have for their opponents.
What do you enjoy doing outside of tennis?
Besides tennis, I really enjoy physical training and almost any kind of sport. Luckily, that also helps me a lot with my tennis. I also love drawing, and I spend a lot of time playing and hanging out with friends who live nearby.
Who would you like to dedicate this interview to?
I would like to dedicate this interview to my parents. They drive me everywhere for tennis five, sometimes even six or seven days a week. They always make sure I have the right food, they learn as much as they can about tennis to help me, and most importantly, they make sure I can always enjoy my sport and have fun doing what I love.
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