Satisfaction with the BBC among its most loyal audiences is showing "signs of waning" for the first time, broadcasting watchdog Ofcom has said.
Older and more affluent people have traditionally used and valued the broadcaster the most.
But Ofcom said: "For the first time, satisfaction levels among audiences who typically use the BBC the most... are beginning to show signs of waning."
That was especially true of the over-55s, according to Ofcom.
"Older audiences in particular are starting to show signs of decreasing satisfaction," the watchdog's third annual report into the BBC said. But over-55s are still "better served than other groups", it added.
The report also said the corporation was "still struggling" to reach younger audiences.
"Average time spent with the BBC each week [by young audiences] now stands at just less than an hour a day," it found.
Young people, the report continued, tend to use BBC iPlayer "when they know what they want to watch, rather than as a destination to browse for new content".
The report said the BBC's "overall reach is still very high, with almost nine in 10 adults consuming its content on a weekly basis".
Yet overall audiences are "in gradual decline", it said, and the corporation's reach among adults has fallen by 5%, from 92% to 87%, over the past three years.
"If audiences do not consider the BBC a core part of their viewing, they may not see value in the licence fee," it suggested.
The report included the BBC's coverage of Kylie Minogue's 2019 Glastonbury set and the Gavin and Stacey Christmas special among its highlights from the year.
It covered the period April 2019 to March 2020, before means testing of the TV licence for over-75s began in August.
The BBC said it welcomed Ofcom's report and its assertion that "audiences value the BBC particularly for distinctive, high-quality, creative programmes, educational content and trusted and accurate news".
The corporation's statement added: "We're committed to delivering great value and meeting the challenges of a fast-changing media landscape."
Ofcom has also published its annual study of diversity in the TV and radio industry, which calls on the sector to broaden the geographic and social make-up of its workforce.