Can I introduce fruits like banana or apple after 6 months..

Yes Pls go ahead. mash them well and you may even used a mesher. Read on @weaning by searching with the word in our search box.;
sharing some Weaning Basics: How And When To Get Started
Weaning In the Initial Months

Yes you can introduce.. banana is the first fruit normally introduced to babies.. then puréed apple... chikoo...