Is it ok not to start menarche at the age of 13...

Is id normal to not having menarch till the age of 13 ?
Yes , it's normal . as the year of meanarch usually starts in a range of 11-16 years old with the mean age is 13 , so there is wide variation between girls when it comes to the age of menarche. 
Signs of puberty ?

1. Thelarche
2. body haid in areas like pubic hair 
3. vaginal discharge before first period
4. Increase og hieght 
5. change of the voice tone 

Advice :
As you're getting closer to the age of puberty , you have to make you life healthier so that you can grow without problems  by eating healthy food, have an hour of sport every morning , and avoid gaining extra wieght , ask for doctor consultation if you period not starting after age of 16