@morten, a 9yo winning most of his matches is no indication of success in this sport. There could be many reasons for that which could evaporate very quickly. Thanks. Well he loses too so this Sounds good. He is ok loosing too. What i do like is that he tries so many things out there.. And I beat him easily the few times we play.. to keep him grounded.lol . No seriously it remains to be seen if he will love the sport long term. He will need some friends to play with on a regular basis..i am not enough if you see what i mean, and tennis is not big in my country.
If he loves the sport, 9yo is a very good age to begin private lessons (unless you coach him yourself). He can spend the next 3 to 4 years developing his stroke technique to an advanced level while enjoying competition tennis from a developmental angle.
Most 9yo and 10yo that I have seen who win everything, and I have seen a lot of them, fall off the perch by the time they are 15. This is because at that age most will lose as much as they win. If they are not used to losing matches, it is very hard for them to continue in the sport mentally especially if they are attracted to other things which tend to become more significant and appealing in the early to middle teenage years.
Of course, there are always exceptions to the rule. I wish you and your son the best of luck going forward.