The default minimum boot jdk version says 1.5.

diff --git a/make/common/shared/Defs-versions.gmk b/make/common/shared/Defs-versions.gmk
--- a/make/common/shared/Defs-versions.gmk
+++ b/make/common/shared/Defs-versions.gmk
@@ -191,7 +191,7 @@
 
 # Generic
 REQUIRED_ANT_VER = 1.6.3
-REQUIRED_BOOT_VER = 1.5
+REQUIRED_BOOT_VER = 1.6
 REQUIRED_FREETYPE_VERSION = 2.3.0
 REQUIRED_MAKE_VER = 3.78
 REQUIRED_UNZIP_VER = 5.12