I don't think 9 is too old at all to start most sports. I also think that any sport where a child has 'missed the boat' if they didn't start intensive training at 3 or 4 years old is not a pleasant thing to commit your child to - if they are going to play sport for pleasure they really ought to be able to choose that sport for themselves and I know at 3 years old most kids have no idea what they want from sport. There were children in my DD's class at school who were competing in gymnastics at a national level at age 8, and they were doing 25+ hours a week training. That's not fair on such a young child.
I love watching the Olympics, and during the last winter olympics I googled the British women's skeleton team, because I had no idea how one would even get into what is effectively competitive tobogganing (I love tobogganing!
) and I found out some very interesting things. Basically the british olympic committee have targeted certain sports as being sports they want britain to excel in. For the summer olympics that includes cycling and rowing. At the winter olympics they are targeting skeleton and speed skating. At no point does a successful candidate for olympic pathway training in any of these sports have to have ever taken part in those sports before. Lizzie Yarnold was a moderately good Pony Club tetrathlete and went along to a selection day out of interest because she had hoped they might consider coaching her for eventing. But they assessed her skillset and sent her skeleton training. I watched Helen Glover win Olympic gold in rowing at the Rio Olympics, as sport she had only taken up at the age of 22. She had seen an advert asking if she could be Britain's next Olympian and put herself forward. Four years later she won gold at London 2012 and is now one of Britain's most successful rowers. Mental attitude and commitment to training is the primary influence here, not what age someone started in a sport at. Without saying what it is, because it is a very, very niche sport, I am current British champion in my sport, a sport I only took up after the age of 40 (Lizzie Yarnold's mum does it too
.)
My kids have chosen an eclectic mix of sports, but all of them have only been chosen from the age of 7-8, and there are still sports they want to give a go. As other people have mentioned, cricket is a great sport to get into if you DS wants to get into a team sport. At 9 he'll still be playing with a softball, and the matches only last about 2 hrs max. Cricket has been a dwindling sport so most clubs are keen to welcome newcomers. It's popularity is on the rise again though after England won the World Cup this year on home turf. It's a very sociable sport to get into and even if your DS hasn't played much there will be spaces for him to play on a team as a fielder, and to improve his game at training sessions so he becomes a better batter/bowler.
If he is set on competitive swimming and you feel the local swimming clubs would pass him by as being too old at 9, look outside the box. DH does open water swimming, and there are often races for children. DS (9) raced down the Thames this summer. DD swims very well but didn't fancy the weed. Both DCs swim weekly with Pony Club and take part in PC triathlons which are running, swimming and pistol shooting. You do need to be a member of the Pony Club to take part in these competitions but you don't need to ride. PC triathlons take place in the winter. And of course there is the standard Triathlon which is running, swimming and cycling too. To help their XC running, and to help DD with her compass reading (which is needed for the sport I do and which DD has made a very impressive debut into this year) we've also just taken up orienteering through the winter too. DD's friend's school do this big time and there's a school league and junior races. They are great fun.
Honestly there is loads he could do. But as others have said, he needs to be aware you can't just start doing something and be a contender a week later. Anything takes time to get good at, but at 9 years old, time is something he has a lot of. Let him choose something and find a way of making it work.