When should we get worried and get a speech therapist when our child hasn’t started talking yet?

Learning how to talk varies from child to child. When I was a first time mummy, I was worried sick that my daughter showed ZERO interest in talking. She wouldn't even mumble and would just keep pointing at things she wanted. I kept reading books to her, and would stop randomly at words that I was so sure she knew but she'd stare at me blankly expecting me to continue. She was about 26 months then. My dad told me to relax and give it a couple of months and to stop forcing it on her and told me to believe it her. I also started letting her mix around with kids her age and I think at about 28 months, she suddenly called me Mama! So happy then. She also starting stringing sentences at a very late age and was only to speak in full sentences at 6 years old when she started kindergarten. She's 7 years old now and so extremely chatty