Irish Citizenship. Proof of Residence question

Hello everyone!
So I need a little help with this sentence:
Now the issue here, is that my boyfriend (born in lithuania, living in ireland since he was a 3yo) was drafted for the Lithuanian army this year. He is now 19, about to be 20 and is applying for the irish citizenship. He does have proof from 2 years, where he went to uni, got a suzi grant and then he also worked over the summer of last year. Now my question is, how is he going to proof any bill or letter from below the age of 18, when he didnt pay any bills or didnt have any of the above written examples? What else can he provide? His parents dont have any of it either.
I am thankful for any example or further question on this.
If anything i said is unclear, please tell me!
Thanks in advance

A letter from his school that he attended stating his address and the years he was in school there,letter from doctors for where is registered and dates that he 1st was signed up in would be a help