Emeritus Pope Benedict XVI, who turns 90 next month, is mentally fit and reading, praying and preaching as he has since his resignation as pope in 2013, according to his closest aide.

The retired pope is also reading the Vatican newspaper every day and watching television news, the aide said.

'Pope Benedict is in good shape,' said German Archbishop Georg Gänswein, the Prefect of the Papal Household for Pope Francis and also private secretary to Pope Benedict.

'What bothers him most are his legs, so he uses a walker for help, and he gets along very well,' Gänswein told Vatican Radio.

'Otherwise, he's quite clear in his head, and quite bright. He participates in everything. He reads, he prays, he listens to music, and he has visitors...Every day he takes a little walk while praying his rosary, so he's doing the same thing he did at the beginning of his time as the pope emeritus.'

Gänswein said that Benedict is still a voracious reader, but refused to be drawn on what the former pope is reading currently.

'Naturally he remains a theologian, but he doesn't just read theology,' Gänswein said, according to Crux.

'Specifically what he's reading, of course, I won't betray, but his interests are very wide.'

Gänswein added that the emeritus pope is still regularly consuming news.

'When his brother is here, the German news is on,' said Gänswein, referring to the emeritus pope's 93-year-old brother, Monsignor Georg Ratzinger.

'If his brother isn't here, then the pope watches the news in Italian, since he lives in Italy,' Gänswein said.

According to Gänswein, Benedict also every day reads the Vatican newspaper, L'Osservatore Romano, and other sources to 'inform himself and know what's going on in the world.'

The retired pope has visitors of 'different nations, different ages, different professions,' Gänswein added.Some are old acquaintances and some he has never met.

Gänswein joked that there are 'so many requests that he ought to work overtime!'

Ratzinger, whose birthday falls on Easter Day this year – 16 April – begins each day with morning Mass.

Each Sunday, Pope Benedict delivers a homily at Mass for his small household, composed of Gänswein and several female members of 'Memores Domini,' a community of consecrated lay women associated with the Communion and Liberation movement.

'We pay attention to what he preaches, because he speaks freely,' Gänswein said. 'He may make some notes, but then he preaches, and we're trying to focus on what he says.'