Speech Therapy

I am wanting to go into the medical field (its kind of a back up if I do not get accepted in the Marshal Service). I was thinking about Occupational Therapist but it seems extremely rigorous and hard to get into. Someone recommended Speech Therapy to me. Can anyone explain what exactly Speech Therapist do and if Communication Disorder is the way to go major wise for it. Also how difficult is the Speech Therapy program? Im sorry for the dumb questions but I cannot find much on SLPs. They work to rehabilitate mainly elderly and adolescents with speech and learning disabilities right?