The correct answer:
Yo tengo 15 años.
Answer:
1. nunca
2. algún
3. nadie
4. ni siquiera
Explanation:
Your answers 1 to 3 are ok.
Answer 4 is wrong.
The difference between "tampoco" and "ni siquiera" is that "tampoco" requires a precedent, that is, before say it you must have said "no".
Ex:
A: ¿Te gusta el cine?
B: No.
A: A mí tampoco.
"Ni siquiera" it is used to express the denial of a "minimum" within more than one possibility.
Example:
"No hay ni siquiera un gato aquí" ("There is not even a dog here") implies one of the following possibilities (or another), depending on the context:
a) They were looking for cats and were disappointed because they didn't find one.
b) They were looking for an animal and were disappointed because they didn't find a cat, which would be the easiest to find.
