A self-published poetry anthology by a 92-year-old Scottish grandfather was outselling Amanda Gorman and Rupi Kaur on Amazon in the UK last week, after his granddaughter appealed to readers for reviews.

Gordon McCulloch self-published his collection, 101 Poems, on 24 March. Covering “a wide range of topics such as love, romance, relationships, religion, prayers, the meaning of life, death and our relationship with God”, it has become a surprise bestseller, last week topping the poetry anthology charts for Amazon in the UK, where it has received more than 1,000 five-star reviews. At time of publication, it is sitting at No 14 on Amazon’s UK poetry charts and No 8 in the US.

The leap in sales came after McCulloch’s granddaughter Jessica Keachie asked her followers on Twitter to take a look at the book in April, writing, “A review would make him so happy.”

Her tweet went viral, receiving almost 300,000 likes as readers around the world replied to say they were snapping up the book. “What started as a family project just so all my grandpa’s poems were in the same place and an attempt at getting a few reviews from family and friends has escalated into an unimaginable dream of his. We only expected 100 books to sell but now his words are all over the world,” Keachie wrote on Twitter, as the book shot up the charts. “I am thankful I’ve been able to put a smile on his face because that was all I wanted.”

McCulloch’s son William told the Guardian that his father was “over the moon” at the sales. “He has been writing poetry for years, and sent it to different places, but always got rejected,” he said.

William’s brother Gordon helped their father self-publish the book and “it just went nuts”, William said. “At his age, it’s one of those things he didn’t think would happen. Now he’s looking around for poems he didn’t use for a sequel.”

William believes the poems, in which his father writes about his life and relationship with his late wife Mary, who died from cancer, have touched a chord with people because “they’re honest”.

“People can relate to them. If you look at the reviews, a lot of people are saying that it reminds them of their grandparents or parents,” he said.

McCulloch lives in Braidwood – “just a wee village, if you pass through and you blink, you’d miss it,” said William – and has been handing out copies of his book to neighbours since sales took off.

“He’s really chuffed, he’s had a wee tear in his eye, these things give him a boost. What I’ve noticed is he’s got a wee spring in his step as well,” he said. “He just looks after his wee pony, that’s basically it. The whole family is over the moon with it. Over the years – this sounds bad – we’ve been subjected to his poetry, we would just say, ‘That’s great Dad, that’s brilliant.’ He’s proved us all wrong.”

Illustrated by McCulloch, 101 Poems includes some poems which “have been written in a manner that will provoke your innermost emotions, while others dig into the amusing side of life”, according to its description on Amazon. But “all have been composed under the auspices of the Muse”.

In “You”, McCulloch writes of how “Because I found you in my life / you made this world for me / a heaven filled with ecstasy / a place worthwhile to be”, adding: “If only for a little time / we spent it both together / I won’t forget I don’t regret / the time we spent together”.

Keachie said that McCulloch wanted to “thank everyone for their unbelievable positivity towards his book”, but said he wouldn’t be commenting further.

“My grandpa is very old and lives a private life because of that this will be the last thing I post about my grandpa’s incredible journey,” she wrote on Twitter. “I hope the love from this gives people comfort and hope that unbelievable things do happen, no dream is too big or too late.”

“It’s fantastic to see the book doing so well and engaging readers around the world,” said Simon Johnson, director of Amazon EU Books. “It’s a tremendous achievement, one that will no doubt inspire many other authors who are looking to fulfil their publishing dreams by self-publishing their books.”