Hissing and growling and the occasional spat is to be expected I think. Big age difference and likely to take longer than with a youngster. Sounds like you are doing just fine
I'm now gonna try and get you posting a pic of your lovely polydactyl Tortie Ember by hijacking your thread with a Ruby pic
Ruby is 5 and a half years old. Only difference we know of is to keep an eye on claws on any extra toes that she doesn't use often. In Ruby's case, we very occasionally need to clip her back dew claws to ensure they don't curl into her pads. Think we've only done it 3 times in her glorious, much loved, five year life.
Will keep an eye peeled for pics of the lovely Ember