Prem, I was a member of the Nagaland U-23 team in 2017. I was a part of Sunrisers Hyderabad development squad at 2013 season too. Since you mentioned that you are a pace bowler, you should read my article on How to become a genuine fast bowler
which is here on Indiastudychannel. The article will be extremely beneficial for you.
Next thing I would like to mention is that you have to make it to your state's U-19 team for Vinoo Mankad trophy and Cooch Behar trophy in order to make it to the India U-19 squad. Vinoo Mankad trophy is BCCI's national U-19 one-day competition, the U-19 version of Vijay Hazare trophy while Cooch Behar is the 4 day U-19 competition which is U-19 equivalent of Ranji trophy.
Now in order to make it to your state U-19 team, you have to go through a lengthy and hectic process. You have to be impressive on 10 out of 10 days until you finally make it because the competition is extremely high these days. Also, it's a process which takes time and patience is the key. So below are some points which explain the road map for making it to the India U-19 team.
1- If your academy has a club registered with your city's league, make sure you make it to the club team first. If you are doing well at the practice games and nets, you might get a chance soon. If your academy does not have a registered club, talk to your coach about it and he might help you with finding a club.
2- Some district associations don't have leagues. They organize tournaments so keep your eyes glued for the local cricket trials. Attend the trials and if you make it to a team via trials, you need to perform well there. If you did well at the district tournament, you will make it to the district team. After the district tournament, most state associations list down top 60 to 90 players of the state for a camp. The camp is held to test your mental as well as physical abilities. You have to be on your toe for the camp matches and practice sessions. If selectors are impressed, you will make it to the State U-19 squad. From there, you have to make sure that you play the Vinoo Mankad U-19 and Cooch Behar U-19 tournaments on a high. If you knock a few wickets down and finish on the top of the table, you have a real chance of making it to the India U-19 team.
3- The process at the grassroot level is different for almost every state and city in India. For example, in Delhi, you can make it to the Delhi U-19 team by doing well in the DDCA league and other age group tournaments, in UP you have to clear a District trial>District games>Zonal team and Zonal Games (Games between top 90 of the state (6 teams of 15 members). The South Indian states have a better ladder system where you have league games from the start and as you perform, you advance. So it depends upon which state you are in. Just find out the way that works in your state (or add me as a friend on ISC and tell me which state you are from so that I can help).
4- As you are just 13, you have a lot of time. Before U-19, you have U-14 and U-16. The U-14 is called Rajsingh Doongarpoor Trophy while U-16 is called Vijay Merchant trophy. So prepare for these two tournaments first. The process is almost the same as mentioned above. If you impress the selectors in these two tournaments, you can just walk in India U-19 team just like Vijay Zol.
5- Read newspapers every day. Follow BCCI social media pages and keep a track of upcoming trials. BCCI organizes special NCA camps for fast bowlers so if you make it to the NCA based on your bowling, you won't need anything else. BCCI will directly recommend your name to your state association and even U-19 India.
6- Keep track of private camps and tournaments. They charge some fee but the knowledge you gain there is valuable. Some organizations like 'Cricket Performance Point' hunt for talented players and get sponsors for them. They track your development and invite you to their camps where you get to meet some ex International cricketers (and current ones too). They share an invaluable amount of knowledge. To know about such camps, you can contact me on my ISC profile. Just drop a text maybe.
Good luck, and always remember that there's no substitute for hard work.