Rescued Mini Schnauzer Too excitable - Too old to neuter?

Question
Hi there! Thank you in advance for helping me with our doggy problem. About 2 months ago, my boyfriend and I adopted a rescued and unneutered older mini schnauzer (was a stray, stayed in a foster home for about 2 wks). We don't know his history and according to the vets, he is estimated to be between 5 and 10 years old (a huge range!).  He's completely attached to us, affectionate and loyal, such a cutie, but has some minor separating anxiety issues which we are gradually working out.

At first he was very quiet, timid, and did not bark. He whimpered and yelped here and there. But he is oh so energetic! He goes on about 3-4 walks / day, about at least 15-20 minutes each. We play catch in the apt, and take him to the doggie run about 1-2x a wk. We are rather worried about his over-excitement when he sees other dogs. As soon as he spots another dog on the street, he will bark, whimper, howl and pull the leash. If I don't let him greet, he will bark and whimper for a good minute or so until the dog vanishes. If I do let him greet the dog, he gets super excited and sometimes freaks out the other dog (or better yet, starts mounting him/her). I tried a few times to distract him with treats before he sees them or make him sit, but he just won't listen. I've heard about the squirt gun method-- is that too harsh to use as a distractor? What else can I do? When he's at the dog run, he finds one dog, becomes totally fixated on him/her, and will not stop mounting him. My dog is on the small side, but that doesn't stop him from mounting a lab or labradoodle. It's kind of embarrassing/amusing (I know we are not supposed to laugh and give him attention). He isn't fixed and we totally believe in spaying/neutering but we are scared that he's too old to go under anesthesia. We originally thought that if he gets exposed to more dogs, he will learn that is an unacceptable behavior. But he doesn't seem to get it- that his over-excitement and his mounting behaviors totally freak other dogs out and they then don't want to play with him. I don't want him to become the social outcast of the dog run (sorry for being dramatic). Would having regular doggie play dates help?

One thing I noticed is that he can get from totally chill/mellow out to super crazy "I am on coke" kind of excited in like 3 seconds, and I have a feeling that may not be the best for him. Is that typical with schnauzers? Aren't they supposed to mellow out with age? He really acts more like a 3 year old than a 9 year old... so we don't believe the vets' estimates.

Again thanks for reading this. Any feedback would be greatly appreciated!

Answer
I once had to have a 13-year-old neutered because of testicular cancer, so, no, yours is not too old. Just be sure the vet has him on a heart monitor during surgery. They will also do blood workups beforehand to make sure that he shouldn't have any problems with the surgery.

Yes, some schnauzers can go from 0-60 in three seconds. They can be ready for anything if they think it is appropriate. The mounting behavior is dominant behavior, so neutering may not change that.

Dog parks are not my favorite places for dogs, as too many smaller dogs have been killed by larger ones. Schnauzers think they are 500# dogs, so they are apt to quickly get in over their heads with the wrong dog. If you can find the right dog or two in the neighborhood, regular play dates can be very beneficial.

Personally, I wouldn't let him greet other dogs when out for a walk. He is walking with YOU and should be paying attention to you. The leash is your key to the Cadillac and you are the one driving the car... not the dog.

You should get him into on-going obedience classes over several months, and start practicing "Nothing in Life is Free" with him. http://k9deb.com/nilif.htm  He needs to learn what behavior is allowable and what is not. Spray bottles work well for many schnauzers as a lot of them do not like water (particularly when sprayed in their face), but a few will think spray bottles are a lovely new game. You will find out quickly which one he is. A quick spray in the face along with a verbal correction can work wonders with the right dog.