Would it be a problem for my citizenship if I didn’t provide a selective number which I was not aware of?

Generally, failure to register for Selective Service because an applicant was unaware of the requirement will not stand in the way of eligibility for naturalization. Information about Selective Service registration must be answered accurately on the naturalization petition; a letter from the Selective Service showing that you now are too old to register should be supplied to the USCIS; and you should be prepared to explain that the failure to comply with your legal obligation to register was due to not knowing of the requirement rather than due to a willing refusal to comply with the law or due to a lack of good moral character. These are just some of the details of importance in the naturalization application process; it would be wise for you to work with an immigration attorney to assure eligibility and to assure proper completion and supply of full supporting documentation in the application process.