I am constantly battling with myself on this subject! Generally, I prefer male dogs to be kept entire for at least a year (especially in the larger breeds) and if the dogs are of a nervous disposition then I think it is extra important as the testosterone can help them cope in situations that might make them anxious. However, many of the male dogs I work with are defensive when around other males and so we often recommend neutering then. I work regularly with a Springer Spaniel called Dexter (who is a personal favourite of mine). He was entire until he was around 18 months and found every male dog offensive and would lay into them. The owners were very reluctant to get him neutered but as he wasn’t really nervous in any other part of his life I was confident that getting him neutered would solve the problem (providing they hadn’t left it to late as his behaviour could quickly have turned into a learnt habit). Long story short, they eventually did get him done and he changed almost over night aNd is now generally friendly and happy around other dogs. I have never seen a change quite that quick but it was obviously the necessary course of action for him.
I try to base my opinion and advice on each individual dog as every case is so different, however my general rule is, if they are fine with other dogs and under a year, keep them entire until they are between a year and 18 months. If they are of a nervous disposition, keep them entire while seeing a behaviourist to try and get them to a confident enough point where removing the testosterone won’t matter as much. If they are defensive with other dogs but otherwise able to cope with every day life, get them done. I always warn owners who choose to keep their dogs entire that other dogs may take offence to them, even if they themselves are friendly enough.
I don’t know how much behaviour training the vets where you live get but over here it isn’t much at all. Most vets seem to push to get male and female dogs done at 6 months regardless of temperament and state of mind. With this in mind I would recommend getting both the opinion of your vet and a behaviourist as you will then get all the medical and behaviour advice you need to make an informed decision.
All this is also based on how responsible I think the owners will be with an entire dog. If I think that they are likely to allow their dogs to mate with a bitch, adding more puppies to the over population, then I will suggest neutering.
I also have to stress to owners regularly that getting their dog neutered is not a guarantee that it will calm down without some impulse control work. In some cases it does help calm them down but I see more cases where it doesn’t make much difference.