You need treatment in two parts. First get tongue tie corrected then get speech therapy for atleast six months. Both part of treatment are necessary. You need to work very hard to correct speech problem not treated for 24 years.

Usually tongue tie does not cause any speech problem. Severe tongue tie can cause dificulty in tongue movements and It's consequences like poor oral hygiene, as tongue movements are needed to keep the mouth clean. Release of tongue tie is a simple operation to free the tongue, can be done, but you will need speech therapy to correct the speech problem. You may also need psychological counseling to boost up your confidence.

I concur with Dr Kaushal's opinion.