Проверьте есть ли ошибки. dear sir/madam, i am interested in becoming a volunteer in education international and i would be grateful if you could give me some further information. first of all, i would appreciate it if you could tell me in any particular locality i will be working. could you also let me know what age you look for young people? i would also like to know what subjects need to be taught. furthermore, i am interested what is included in free accommodation. finally, could you tell me how much will i earn? thank you in advance for your assistance. i look forward to your reply. yours faithfully,

То, что выделено жирным - убрать. То, что жирным и курсивом - вставить ))) Плохо, что тут зачёркивания нет, было бы понятней.
Dear Sir/Madam,
I am interested in becoming a volunteer in (я бы написала of и поставила артикль the) Education International and I would be grateful if you could give me (используй supply вместо give me - звучит лучше) some (не нужно здесь some) further information on the following.
First of all, I would appreciate it if you could tell me in any what particular place locality I will be working in. Could you also let me know young people of what age you are looking for. what age you look for young people? I would also like to know what subjects need to be taught. Furthermore, I am interested would like to clarify what is included in into free accommodation. Finally, could you tell me how much will I earn? I will learn.
Thank you in advance for your assistance. I look forward to your reply.
Yours faithfully,

По-моему там, где есть would и if - could уже не надо. просто if you tell me

what age of young people you are looking for

а так норм, пять бы поставила.