When will we lose our lateral incisors?

Hopefully never. Your adult lateral incisors should last you a lifetime. There are no other teeth to erupt at your age.
About age 7-8. Baby lateral incisors exfoliate (fall out) about 7-8. All baby teeth should have exfoliated by about age 12. Permanent teeth that replace baby teeth are designed to last, with proper care, for a lifetime. If you still have baby teeth present either permanent teeth are congenitally missing or are impacted. See your dentist for examination, x-rays, and discussion of this issue.