diff --git a/utils.R b/utils.R
index 9a6d88a..188a775 100644
--- a/utils.R
+++ b/utils.R
@@ -71,6 +71,11 @@ sma_load_data <- function(file) {
 	sma$thalidomid <- as.logical(sma$thalidomid)
 	sma$bortezomib <- as.logical(sma$bortezomib)
 
+	#
+	# Limit to patients which are at least 16.0 years old at time
+	# of transplantation.
+	sma <- filter(sma, asct_age >= 16.0)
+
 	return(sma)
 }