SQL to delete old Magento Abandoned Cart Entries: Quote (sales_flat_quote), Quote Item (sales_flat_quote_item), Quote Item Options (sales_flat_quote_item_option), Quote Address (sales_flat_quote_address), and Quote Payment (sales_flat_quote_payment). Does not clear out sales_flat_quote_address_item but you can follow same logic.

clear_magento_abandoned_cart.sql

DELETE FROM sales_flat_quote_shipping_rate WHERE address_id IN (
	SELECT a.address_id
	FROM sales_flat_quote q, sales_flat_quote_address a
	WHERE a.quote_id = q.entity_id AND q.created_at < '2016-12-31 23:23:59'
	);
	
DELETE FROM sales_flat_quote_address WHERE quote_id IN (
	SELECT quote_id FROM sales_flat_quote WHERE created_at < '2016-12-31 23:23:59'
	);

DELETE FROM sales_flat_quote_payment WHERE quote_id IN (
	SELECT entity_id FROM sales_flat_quote WHERE created_at < '2016-12-31 23:23:59'
	);
	
DELETE FROM sales_flat_quote_item_option WHERE item_id IN (
	SELECT i.item_id
	FROM sales_flat_quote q, sales_flat_quote_item i
	WHERE i.quote_id = q.entity_id AND q.created_at < '2016-12-31 23:23:59'
	);

DELETE FROM sales_flat_quote_item WHERE quote_id IN (
	SELECT entity_id FROM sales_flat_quote WHERE created_at < '2016-12-31 23:23:59'
	);

/*
DELETE FROM personalize WHERE quote_id IN (
	SELECT entity_id FROM sales_flat_quote WHERE created_at < '2016-12-31 23:23:59'
	);
*/
	
DELETE FROM sales_flat_quote WHERE created_at < '2016-12-31 23:23:59';