BuddyPress 2.5 will require WordPress 3.9

Previously: https://bpdevel.wordpress.com/2015/08/06/wp-version-compatibility-guidelines/

In accordance with our WP compatibility guidelines, we’ll be dropping official support for WP 3.8 in BuddyPress 2.5. For more details, see #6805.

#2-5, #6805, #wp-requirements