
I'm no expert and others will come on with better advice I'm sure, but my boy is 21 months old now and has been similar so I thought I would share.
He is the absolute Casanova of the gundog world, my friend said if he had a theme tune as he walked it would be "
I'm sexy and I know it". However there was nothing punchy or sharp about him you could just see he was becoming a man and wanted everyone to know, as you say! And he was my first male dog, so I was a bit flummoxed.
It started around the same age as yours, and I posted on here that I was thinking of having him implanted with suprelorin, but I decided to wait. I attend a lot of doggy events, so I couldn't withdraw him even if I wanted to. I decided to have him around a lot of dogs, but be a little more fussy with his socialising. That is to say, every dog that approached him, I've asked the owner "are they friendly" first (something which I still and always will do)- the last thing you want is a dog to pick on him when he's already on his tiptoes! I also wouldn't let him say hello to anything without him checking in with me. He lost a certain amount of freedom to explore these things and make up his own mind. So I spent some time teaching a new release cue, by hanging around dogs which were under control- ie. on a lead at a show, and clicking and rewarding the "checking in"- ie. looking at me, followed by releasing to say hello (if appropriate), followed by a "come away" command which is clicked and rewarded. I moved this on to a long training line on walks. My boy has one of those faces that a lot of male dogs just want to punch (he is big, black and confident)! But he doesn't take any notice, I have had dogs fly at him, and he just looks at me, I say "did that dog swear at you?" and he'll just go "yeah, what was that guy's problem?!" and move along.
I haven't got it cracked totally, he will still run up to dogs occasionally if I'm stupidly not prepared and will have a flirt, but what I thought had the potential to become a problem was/is nothing more than teenage hormones and as many advised me at the time it is passing, I think you just need to protect him from those situations until he is through it. Of course it must be that some
don't come through it, but as others advised me back then, training (and time) first, then think about alternatives.
Personally... I would not tell him off. You are only providing more negative to what he's already feeling in my opinion. If it's nothing more than a little grumble then you should be able to say I recognise your issue with that dog and use the "come away" command and try to move far enough away that you can at least break his gaze. Simple distraction, and acknowledgement that his arousal has gone over threshold. But you will want to do it quickly and confidently because anything like pressure on the collar or you hesitating is probably going to make him more prickly and grumbley. You should be able to read his body language and stop it from getting to that point though, even if you have to ask the owner from a distance if the other dog is a male, and then choose to keep your distance (training opportunity!). In the same way I can spot a dog who is about to have a pop at mine, and happily say to him "come on let's go over here", he now knows (I hope) that he doesn't have to deal with any situation, I will handle it and he'll be fine. I attend a hall once a month with him, there are three other dogs, a spayed female and two entire males all of whom want to punch him in the face, I can have him off lead with the others snarling, bouncing and barking and he can happily carry on working, but 6 months ago his tiptoed stance and stiff body had me worried that he might snap back.
Your boy certainly doesn't sound at the point of no return, and I'm sure is well capable of picking up the tools needed to cope with these situations :) My boy's best friend in the whole world is another entire male, and they never have a cross word between them.