I'm currently 13, i'm not able to cum and my testicles and penis haven't grown

The reason for that is quite simple, puberty doesn't happen over night!

Every male/female starts puberty at different age some early and some late you all also in through puberty at different stages to each other, some guys may notice there penis and testicles get larger but don't have pubic or body hair till later just like some girls start by growing breasts first and other don't but have other changes first, puberty starts around the age of 11 for most and will carry on right throughout your teen years so don't worry your no different to anyone else.

It happened to me when i was 13 till I got to puberty but how I use to masturbate is i went into my older sisters closet and I got her chiffon dresses. I rubbed my penis in the dress but then i wanted to wear the dress and then rub my penis in it and man did it feel so good