neutering older dogs

Question
Hi.

I found my dog, Jaadhu, (who seems like he could be a mix of black lab and Australian shepherd) almost a decade ago when he was about 5 months old.  I have never neutered him because of various reasons I now regret including vets who really didn't seem to think it was that important since he was such a passive animal.  Overall, he's been spirited, gentle and not aggressive.  Mostly, he's a well behaved, obedient, sensitive and communicative pet.  He's also very healthy and fit and constantly runs and plays fetch.  Besides the graying hairs and slowly declining eyes and teeth, you would think he was half his age.
However, it's nerve racking taking him to a dog park because I'm never sure how other dogs (especially males about his size and larger) are going to react to him.  He seems to get along pretty well with most females, smaller dogs, a few cats (!) and really submissive males.  However, over the years he's gotten a bit more grumpy and defensive.  He almost never starts fights and tends to ignore most dogs or to raise his shackles but then slink away to avoid trouble. But other males do attack him and if they get to him he does not submit instantly but fights back, at least in the beginning.  He has also growled at rambunctious puppies to put them in their place.  Is it too late to neuter him at 10 years old?  What are the risks associated with neutering an older dog?  I feel like I've done him a grave injustice because it's probably a lose-lose situation.  If it is too late, then are there other things I could do to help the situation?  I realize that my own tension and anxiety when other dogs come bounding up to him plays a huge part in facilitating any fights he gets into.  Because of my own fear, I feel like I keep him from socializing with other dogs just to avoid a potentially aggressive situation.  Is there anything I can do to change any of this?

Answer
I don't know that it is a problem to neuter an older dog.  Responsible breeding programs retire and neuter their studs at about that age.  Doing so will still reduce the chances of cancer as well as help with the behavior.  You may not see it right away.  

You are correct about your emotions being part of the problem.  You do need to do your best to relax.