Joseph Ray Dunbar, the youngest of the miners, celebrated his 17th birthday the day before heading down the mine.
His mother, Pip, said Joseph was so excited about his new job that he convinced his boss to let him start on Friday - instead of the following week.
She said despite friends wanting to celebrate with him, Joseph stayed home the night of his birthday because he knew Friday would be his big day.
"His mates wanted him to go out that night, but he said, 'I'm staying in. I have work in the morning'. He was so chuffed."
The next day, Joseph went to Pike River, where Ms Timms' brother-in-law escorted him inside for a quick tour.
They came back out and the brother-in-law gave Joseph a thumbs-up before leaving.
Joseph, bubbling with enthusiasm, grinned from ear to ear and returned the thumbs-up before disappearing into the mine.
"He wanted to do this for a very long time," Ms Timms said.
She said becoming a miner had become Joseph's top goal after the family moved from Christchurch to Greymouth. But first he had to turn 17.
"It meant everything. He set himself a goal, and achieving that goal meant everything to him. It meant he was going to travel with the company, take him different places.
"He was absolutely stoked. He was excited, he was ecstatic."
Joseph had previously worked at a local supermarket, but working at the mine would give him an opportunity to have a career. He started as an offsider, with a view to becoming a driller in a year or two.
Ms Timms said her partner, Gary Campbell, "just knew that Joseph could do it".
"[Joseph] texted him and just said how thankful he was and grateful he was and he would not let him down."
Friends at school said Joseph was the class clown - and often got into a bit of trouble.
Ms Timms said he "had to just grow up a little bit" before starting work. Her son was a funny, cheeky, kind, caring and loyal boy.
She said the wait to begin the rescue bid had been frustrating, but she understood why.
"They can't just rush in there because, I know, right from the word go, I know how it works ... If the oxygen rushes in and it hits that methane, then bam, they're gone, another blast."
She said the day of her only child's 17th birthday would remain her most special memory.
"We spent the whole day together.
"It's going to be my best memory to live by. We were very close. He was my baby. He was my world."
Joseph's former employer, Fresh Choice supermarket owner Chris Ward, told the Greymouth Star the teenager was very popular with supermarket staff and customers.
"He always had a good word when passing in the corridor or catching up in the smoko room. He was the sort of kid you could sit down and shoot the breeze with," Mr Ward said.
"It's terrible, really hard, to think of him down there. But it's not hard to imagine him busting a gut to get down there. It's consistent with the Joseph Dunbar I know."
His former workmates at the supermarket had been posting messages of support on Facebook, Mr Ward said.