Please Advise whether to Apply for ILR for my parents

my parents came to england in 1966 and studied and had kids in england. and as student my dad was on a visa and had temporary conditions to remain in england whilst he was a student, after about 7 years in 1972 his passport was stamped that the temporary conditions has been cancelled. my lived and worked here in england, however after given birth to us in england, we went back to africa in 1973. we (kids) are british citizen by births, but my parents have not applied for their citizenship, please can somebody advise me on what to do. my parents are now over 65 years.

See also Older dependent relatives.