Is this a good start for an aspiring artist?

You are very talented! At 15 years old, that is very impressive :D Your value is good but concentrate on providing more for the finer details such as the outlining hairs of the hamster, the facial fur and the ears. Your composition overall is a pleasure to look at but concentrate on the symmetry of the hamster's face. It is a very nice piece! If you have time, you should try different compositions of the hamster on different media! White chalk or pastel on black paper would look very nice for this little guy :)