Wiktionary
big old
a. (context US idiomatic informal chiefly Southern US English) Emphatically or impressively big; really big. alt. (context US idiomatic informal chiefly Southern US English) Emphatically or impressively big; really big.
Usage examples of "big old".
He always imagined growing up back in the 1950s in some kind of traditional family in a big old mansion.
He has a jaunty bandanna tied around his neck and appears to be wearing a big old doggy grin.