Experience with speech therapy at 17, does it help?

Hi, I'm 17, and i have a slight lisp, or well, a bit of a speech impediment really, not so much lisp specifically... I just sound 'funny'. Its nothing drastic, I am understandable when I speak, but, you know, its there. Its never bothered me much in the past, and I have gone to speech therapy in the past, at a very young age, but never continued after moving away. My younger sister has this as well, however hers is much more drastic, dont know if that detail means anything to anyone, but I guess it runs in the family. Lately I've been considering returning to speech therapy. I attend an international school, and am taking part in the rigorous international baccalaureate course, and I was just thinking, later with jobs, job interviews, giving presentations, meeting people, I dont want people to be distracted by the way I talk, or notice my way of talking before me. Anyway, I wanted to know if anyone has experience with speech therapy at an older age. Thanks!