
Tests apart (and that would depend on the age when testing can be done), most breeders (and this is in my breed) would start teaching a potential stud dog his 'trade' by around a year. Using him on a suitable bitch of their own first to see what he produces. After that first go, they'd then rest him off from stud work, and concentrate on a show career and if he's successful enough, maybe offer him at limited stud 'to approved bitches'. Having a stud dog is almost as much a responsibility (some might say more given how much many popular studs have on a breed, especially if over-used!) as having a producing female.
But as always, ONLY top quality dogs should ever be used in a breeding programme. Otherwise it's far better to keep them as a much-loved pet. And there's always the very real possibility that once used, he will be looking for the next one always. Opening Pandora's Box.
The person you should be in touch with re stud work, is his breeder (assuming they are reputable knowledgeable people). Other than the show ring to test his quality, again provided they are honest, the breeder should assess your male now he's through the puppy stages and tell you whether in their opinion, he's worthy of being used at stud (and about the testing needed for his breed, which would be more than just a health check by a vet). You should be aware that knowledgeable breeders with bitches may well prefer to go to the sire of your dog - if that sire is throwing good offspring. And there's another thing - good breeders don't sell their immature stock without endorsments which will have to be lifted, by them, before any puppies they produce can be KC Registered. If he's good enough (superior to anything she has in her kennel) she might be interested in using him herself.