It's absolutely normal that colour of teeth change as we become older,its called ageing.like our hair becomes white it's normal that colour of enamel changes from pearl white to yellowish white,but its bad not to brush teeth as it may cause gums to bleed like urs I guess there may be inflammation of gingiva also.Get the teeth cleaned from your dentist.
Next Steps
use gumex gum pain to massage gently on gingiva,along with Clohex mouthwash twice a day for gargle.
Health Tips
Visit ur dentist every 6months.