I am running a blog of skateboard parts, safety gears, and essential accessories from 6 months but still unable to find the mistakes why the website isn't getting ranked or traffic. But one thing that i have read is the new websites having age of around of 4 to 6 months get into the SANDBOX.

This might be your course after getting some traffic as my website has also got some traffic but it seems like it is in sandbox

As long as i have found the answer per my experience is the spammed links.
You might be using any spams tool for creating backlinks. Or there was no specific strategy for OFF--page. Like the anchors distribution as well as the websites from where you are getting the links.

I still remember, i had a website of client based on the superlative skating gears like best skateboard decks and wheels were facing the same issue.

I just fixed some spammed backlinks and take them out of our website by disavowing in google disavow tool. The site was getting ranked again after a month.

Reducing the spam score isn't a big deal, As i have done it recently for my skating play.

1- You just need to enter the website in MOZ spam score checker
2- You will see the list below, export it to the Excel or CSV
3- Now you will see all the websites
4- Applying the filter would make it easy to find the spams websites
5- Apply filter for show the sites having higher than 30 or 20 score.
6- Now put them these sites is google disavow tool
7- Always keep in mind that those sites might be spams but there can be authority and that authority might be proving as lucrative for you
8- Take step carefully

Now you will be able to get the job done.