Will a literary agent be less likely to accept a story because the writer is in their teens?

No, a literary agent is not necessarily less likely to accept a story because the writer is in their teens. What matters most to agents is the quality of the writing, the originality of the story, and its marketability. Some agents and publishers even find it appealing to discover young talent. If the story is well-written and has potential, age won't be a major factor. However, younger writers may face challenges like building writing experience, but that won't deter a good agent if the work is promising.