
Personally I don't think castration would help, unless it's bitch scent he's following - and it doesn't sound like it is. My dobe boy was exactly the same at around 10 months, and I had him neutered to counter it - it did no good whatsoever, and it was too early I think. As a result I had a dog that still wandered off, but also ended up as an adult on the lean side build-wise as he hadn't finished filling out before he was done. If you do get him done I'd wait a little longer, till he's physically mature.
Now, your pup - I'd have him on a long line TBH. You say he won't learn a good recall if you have to go and fetch him - well, he's certainly not going to learn a good recall if he gets umpteen opportunities to ignore it (your repeated whistling and calling with no response, even if he comes eventually), and a very good reward for doing so (interacting with other dogs/people)! I'd say at the moment he's learning quite nicely to do his own thing :p
I'd start retraining it indoors with a new cue (as he's learned to ignore the normal one), use whatever really gets him going - chicken, liver, squeaky toy, etc - and just give the cue and the reward straight after, a couple dozen times a day for a couple of weeks. Then take it outside - somewhere uninteresting (or the least interesting to him) - and repeat. Only reward for responses, don't repeat the cue more than once, and don't give it if you think he's going to ignore it. When he's excellent at that, take it somewhere a little more distracting, and repeat! Keep it up, building the distraction as he gets good at each stage (always on a lead/long line), and only when you're confident that he'll recall from whatever's distracting him out on your walks, let him off lead again.
Remember to practice his recall throughout his life - don't only use it when you need to, use it when he's just pottering about or your playing so he doesn't only associate it with a tempting distraction - that should make it stronger. And personally I always reward for recalls - some people do it randomly, but I think that's down to the individual dog. I find mine recall more strongly if they always get a tasty treat, but some dogs are better if they don't know which recall will be rewarded - that's up to you to work out! Oh, vary the rewards - the best things can get boring after a while, as you already know :)
Something I also find helps is to have the strong recall on a cue that I don't use too often - apart from emergencies and the odd practice as I've mentioned - I use an acme whistle for it. In normal walking situations I use their names and I whistle myself for a slightly better recall, but I save the acme for the most part - it makes it more unique (think "background noise" - if they hear something often enough, it can get tuned out) and more special.