Hi Flynn's people, welcome. What was the reason for his amputation?

Typically we see that senior dogs take longer to recuperate than younger ones. You're right, every dog is different, each with unique ways they recover. But what we can tell you is this:

When a dog is having a hard time standing after surgery, often it's because the pain meds aren't dialed in yet. Many are super sensitive to the pain meds, which make them woozy. Has he ever had surgery before and if so, how was he then with the pain control?

I'm not saying to stop or reduce his meds, but let your vet know what's going on so they can come up with a strategy that provides relief while still allowing him to get around better. Can you call them today? Sometimes just a slight tweak in the dosage and timing helps tremendously. 

What meds is he on? How much, and how often?

Another things is that if he was given a Fentanyl patch, you should see a little sparkle coming back today, they only last 72 hours.

Also, what are your floors like? Do you have traction down for him to give him confidence when he gets around? 

It's so hard to know when to baby and when to let go and allow them to do their own thing. You are on the right track though, so keep it up!