EBF baby gaining too much weight?

So my baby is nearly 2 months old, and is already 18 pounds (!). He was 10# at birth (but was born two weeks “late”), so he’s gaining over a pound a week. He’s exclusively breast fed on demand, and I’ve heard that EBF babies can grow more quickly than the averages you read about online - but this seems like way more/faster weight gain than anything I’ve heard about... We have his two month appt next week, but I’m hoping y’all can put my mind at ease until then. Can anyone chime in?