### Database Schema:
CREATE TABLE user_reviews (
	App	TEXT	NULL,
	Translated_Review	TEXT	NULL,
	Sentiment	TEXT	NULL,
	Sentiment_Polarity	TEXT	NULL,
	Sentiment_Subjectivity	TEXT	NULL,
	foreign key (App) references playstore (App)
);

CREATE TABLE playstore (
	App	TEXT	NULL,
	Category	TEXT	NULL,
	Rating	REAL	NULL,
	Reviews	INTEGER	NULL,
	Size	TEXT	NULL,
	Installs	TEXT	NULL,
	Type	TEXT	NULL,
	Price	TEXT	NULL,
	`Content Rating`	TEXT	NULL,
	Genres	TEXT	NULL
);

### User's Query:
What is the percentage for free application with a rating 4.5 and above have not been updated since 2018?

### Extra Knowledge:
paid refers to Type = 'Paid'; application refers to App; Rating>4.5; Last Updated>'2018; percentage = DIVIDE(SUM(Genres = 'Mature 17+' and Rating>4.5 and substr("Last Updated",-4,4)>'2018' )), (COUNT(App)) as percent;
SELECT CAST(SUM(CASE WHEN SUBSTR('Last Updated', -4) > '2018' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(App) PER FROM playstore WHERE Type = 'Free' AND Rating >= 4.5