the problem with this specific Image is that the only thing that makes this a "Granny" would be the walker. to sum it up... she doesn't really look the part as much as she could.
she looks like a young women pretending to be her grandmother.
to improve the image i would do a couple of things.
on the model side i would Add some wrinkles to her face... maybe define her cheekbones. possibly make her eyes squint. since she is elderly her nose probably needs to be slightly bigger since thats the only part of our body that continues to grow past our 20s though compared to men its more subtle in women.
on the pose i would make her hunched over abit more.
on the materials (assuming you want to keep thinks simple) you really need to add a highlight to her eyes... Cartoon charters tend to look dead if they dont have highlights in there eyes.
all in all it needs some work... you need to focus on figuring out how to breath life into your characters... one way to do that is to emulate reality.... things like Weight, Force.... and well basically anything that will affect how your character will look and behave if they were alive..
keep at it! never stop practicing.
though on a more general note it seems you are falling into a pitfall...
taking a glance at your channel you seem to dabble in everything..... little bit of music... little bit of 2d work little bit of 3d work... and probably a couple of other things.
a Jack of all Trades, master of none isnt something you want to be.
a Jack of all Trades, Master of ONE is.
basically you can study other things if you really want to... but you need to pick something and work your tail off at that.... whether that is Music, Drawing or computer graphics.
strive to be a Jack of all Trades but a Master of ONE.
Best of luck!