"My grandmother is 101 years old."
祖母 (sobo) is a polite word you use to refer to your own grandmother, usually outside of your family/friends. おばあさん (obaasan) is what you would call another person's grandmother, or what you would call your own grandmother.
ばば (baba) means old woman (and is also an uncommon way to read 祖母).
ばあば (baaba) is a word that children use to call their grandmothers.
ババー (babaa) is super rude and the only reason I bring it up is to emphasize the importance of long vowels (please don't mistakenly call a hapless old woman a "hag").
after reading this comments section... not even kidding, for one solid year i've always thought grandmother was そば (soba, aka. noodles), not そぼ (sobo).
skidaddle skidoodle, my grandma's a noodle (」°—°)」
no wonder people gave me weird looks when i speak to them in my already broken japanese