Yeah, when my family dog was 17 and I was about your age, she clearly had a few serious things going on with her and euthanizing very well could have been the right thing for her, which we did, but in retrospect it bothered me very much that we didn't get her new symptoms diagnosed, just the recommendation for euthanasia because her quality of life was very poor.  Especially after learning about all the things they can do for dogs these days (both with conventional and holistic medicine) through my experience with my  next dog, Yoda, (who had cancer) I couldn't help but wonder if I had more information or asked for a referral to our local University's veterinary school, maybe there would have been more options for her.  (Though maybe they wouldn't have been financially feasible, which is a very hard fact of life).  Anyway, to sum up, if they are just telling you euthanisa is it and aren't telling you much else, I would recommend pressing your vet for what exactly is wrong with Toby.  Then tell your vet you need to think about it (totally understandable) and you can do your own research for other options, if you're not satisfied.  Good luck!

Ok, once more for my famous soap box - get a second opinion.  Not all vets have the same approach, and you may find one you are more in line with.  If by chance they both tell you the same thing, it may be time to listen.

Sending lots of good thoughts yours way, I know you are scared, and I know you aren't ready to let go.  Please remember 16 years is an long life for a dog and I know Toby has a happy life with someone who worries about him and wants the best for him.  Good luck as you fight to find the right answers.

Welcome to the family. I'm gonna hop on Shanna's bus, if you don't think your vet is giving you every option, second opinions can result in alot more time for some dogs, her Trouble is a living example, over 2 years now. And if you do decide to get a second, I would try to find a younger vet that might have knowledge of some newer procedures, technologies or treatments, some of the older guys tend to resist new ideas. That being said, no matter who you decide to have treat Toby, have them explain to you what is happening, why it's happening and the outcome, time frame, cost of any resulting treatments, don't be intimidated by any vet, there are no stupid questions. Now, let me say, as much as you want to get him going again, and only a thorough examination and x-rays, mri's or whatever will you find that out, it may be determined they can't help him. There is a point where no amount of treatment, medication, or therapy will help. One of the things you will find here is that top on everyones list here is quality of life, and as traumatic and gut wrenching as some decisions are, keep that in mind no matter what you find out. Believe me when I say there are a whole lot of people here who have had their hearts ripped out because cancer or illness took there best friend way to early, so noone here will tell you to do something without knowing the results of what they are saying. Don't give up yet, you may find his problem is comletely treatable, good luck, paws up, Spirit Gus and Dan  

Everyone else has already said what I would have so just let me say that I will be praying for you and your boy, Toby.  Please let us know what the vet says.