No dog is too old to benefit from training.

Too old is when they can't walk any more.

No, dogs are never too old to learn.

They're never too old. I adopted a 2 year old dog and took her through training. When she was 7 we went through again just so she'd stay active.

If it's a larger breed dog and older, then you may want to skip puppy kindergarten – where they work on socializiation, etc. – and start with a basic obedience class.

Never too old. My dad got a stubborn-as-nails old Bloodhound/Bluetick cross from the shelter who had been abused, and with gentle training and professional instruction, was able to get a dog who sat, stayed, came, and layed (even if it wasn't on the first try… XD).

Too old? When she can't get up to move any more.

Despite the common aphorism, you most certainly CAN teach an old dog new tricks, including obedience.

A dog is too old when it can't PHYSICALLY withstand the requirements of the class.

Six months is not even CLOSE to too old. You would benefit greatly from a class, specially if she has never been taught anything before now.

The old saying, "You can't teach an old dog a new trick" is false (as are many old sayings for dogs). A dog can learn to do anything if you are committed. Granted, I won't say it's easy to teach an old dog that's already used to a certain way of behaving as it would be teaching a puppy that is a blank canvas.

But your dog is still a puppy, so she should catch on very quickly.