Peshi and Seva

that certain singh should restrain from doing any sewa(unless the punj pyare have told them to do sewa as their tankah) until that singh has completed his tankah/sewa

Doing sewa in the panj is up to the sangat if they think you are good for the sewa gursikhs/sangat will choose you. If you pesh for doing a dhil or bujjar kurehat and the punj pyare mention that you cant do sewa in the punj you have to follow that hukam

From my understand and from what I've seen, those that get pesh are usually not able to do seva in the panj pyare. I've seen extremely chardikala Singhs who have done this seva for years, but later on had to get pesh for more "innocent" reasons like a medical surgery, etc. and so were no longer able to do the seva anymore. This is just what I've learned from my sangat though.

As for the taking amrit at a young age and getting pesh as on adult situation, I know many people wouldn't consider that to be a 'special circumstance' because anyone that takes Amrit should be fully aware of the responsibility they are taking on by receiving Amrit. Just because one was young when they got amrit probably wouldn't really put them in a position to receive a lesser tankha for their dhils. Growing up and just 'being a teenager' isn't really e an excuse to get out of the mistakes you have made. If one is wanting to receive Amrit, they should fully understand the huge responsibility and privilege that they must carry going forward, no matter how old they are.

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Can one of the siane Singhs on here shed some light on rehat of doing seva after peshi and completing tankha.

I am not really a Siaana Singh. If a person is yet completing Tankhah given by Panj Pyaare, he/she is not supposed to do the Parmukh Sevas reserved for Tyaar Bar Tyaar Gursikhs, i.e. Akhand Paath Seva, Degh & Langar Seva, Kirtan Seva and any Seva in Amrit Sanchar (Panj Pyare or Naam Drir Seva). Seva of cleaning Joray (shoes), other cleaning Seva in Gurudwara, doing Seva of Jhoothe Bhande is permitted, rather desirable.

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If someone takes amrit as a child/teenager, commits a bujjar kurehit and completes peshi / tankha as an adult, what sevas are they restricted from doing?

I heard they cannot do seva in punj during amrit sachar, does this stand for above scenario as well (taking amrit in young age and peshi as adult)? What about pahradar or granthi during amrit sachar?

In case of intentional Bajjar Kurehat, the person cannot do Seva in Amrit Sanchar as Panj Pyaare, Taabiya Singh or Pehredaar Singh. Senior Gursikhs in Jatha suggest that persons peshed for serious Bajjar Kurehats (e.g., illicit relations) should not do Keertan or Akhand Paath Seva for some time, maybe months, even after completing Takhah. Because they represent the Jatha in Samagams in front of the public.

In case of unintentional and unavoidable Bajjar Kurehat (commonly, removal of Kes due to surgery), the abovementioned conditions do not apply.

There is no black and white on this. It is usually decided on a case by case basis. But both scenarios apply even if the person took Amrit in young age and peshed as an adult.

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What about receiving Panja di degh after diwan? Seva in panj for nishan sahib seva or making a gurmatta?

Again depends on the case. If the person has completed Takhah and is now in a good standing in their Jeevan, it seems alright to do so. If the person is still not back to Chardikala, then they should refrain from these Sevas.

Just to add, my last point may not be agreeable. Gurmukhs are welcome to correct me.