All airlines seem to have specific policies on exit rows.

On United Premier Exec (Gold) and 1K members (and no others lower in status AFAIK) may be allocated exits 330 days in advance. No questions asked. Computer will not let phone agent allocate these unless that status is entered and recognised.

Of course on day of travel if check-in staffer (or on board purser) determines exit row pax is either incapable or too infirm to handle that responsibility you may be re-seated.)

On a 747 on a 14/15 hour flight in coach that exit row makes Gold status weight its weight in ......

I was top level elite on CO for about 5 years in mid 90s and mostly flew coach to the USA, and in those days anyway, could always get exits pre-allocated.