Breast milk in Bottles at 5/6 Mo.

Friends, I would appreciate some guidance. My son gets bottles of expressed breast milk when I work 3 days a week. Typically I am gone 6 hours; I leave three to four 4-ounce bottles. More often than not he only takes 3 of them. Today, however, my mom said he guzzled three 4-ounce bottles plus an additional 3 ounces within 4.5 hours! My mom knows to pace feed and all that jazz; we haven’t had any issues with over feeding. She was shocked by his appetite and understandably relieved when I got home because he was getting adamant with his hunger cues. Is this a sign to start solids (oatmeal mixed with breast milk)? I was gonna wait until 6 months (in 10 days) but maybe he is ready now? Or should I up his bottles to 5 ounces? Or both? Any help would be much appreciated.