13 year mature and cant win full erection?

is that normal?

Answers: Well it's not the average. There can be several cause to why you can't:
1) Poor blood flow.
2) You just hit puberty, during the precipitate stages of puberty a full erection is something that's difficult to achieve.
3) You lost interest surrounded by things of the sexual norm?
If it's number 2, just loaf a few months or something. You can also ask your pediatrician about that too.