With his greying hair and diminutive stature, Mr Zhen is an odd sight among the young kids at the video game arcade.
Thrice every week, he joins others at a shoot-'em-up game called Fish Hunter.
A maximum of six to eight players can play together on a tabletop arcade machine, casting virtual nets to catch fish on the large screen.
Mr Zhen, 70, declines to reveal his full name as his wife and children are unaware that he has spent a lot of time and money at the arcade.
He estimates that he has spent at least $30,000 over the past seven years, forking out $50 each time he goes to the arcade at Causeway Point in Woodlands.
There, he sits on a cushioned chair and starts hitting away at buttons for around six hours or until he gets tired.
The money he spends comes from his savings but he says he is hooked.
Mr Zhen said he still has a debt of more than $10,000 from a business that failed years ago.
He said in Mandarin: "Actually, $30,000 would be a low estimate of how much I've spent playing. I can't remember when I started playing this.
"It could have been worse. I could be losing more money gambling in a casino but I'm not.
"This helps me keep my mind active."
When asked why he would not pay off his debt first, he brushed off the question and said he would "rather not think about it".
Mr Zhen is not yet retired. He still works as a part-time delivery driver and earns more than $1,000 a month.
Of that, an average of $300 would be spent on topping up the charge card that he uses to play on the machine.
An addiction specialist said this form of compulsive behaviour can be difficult to remedy if family members do not fully understand the situation.
"But my family knows I'm here, it's not like I'm missing or anything," he said.
Mr Zhen is not alone.
Other players The New Paper spoke to have also spent thousands of dollars on Fish Hunter, although none came close to how much Mr Zhen has spent.
Lim Siew Hong, a housewife in her 50s, said: "It's great.
"I get to meet other friends playing this game.
"It beats staying at home all day."
Madam Lim has spent around $2,000 on the game since she started playing it around five years ago.
"It is highly addictive," she said. "I just can't stop."
At Serangoon's Nex shopping mall, she joins a small crowd of other senior players quietly plugging away at the game, casting virtual nets on the screen.
But even when they catch the biggest fish - it could be a whale, shark or lobster - there is nary any reaction on their faces.
It is the machine that does the celebration for them with bright, flashing lights and the sound of gold coins raining down on them.
It is not a new phenomenon.
Fish Hunter first arrived in video game arcades here around a decade ago and proved to be a hit with older folk.
Arcade operator TKA Amusement, which runs the Virtualand chain of arcades, said there were fewer seniors in the arcades 10 years ago.
But in 2014, they made up around 20 per cent of the arcade-going crowd, its founder Tan Kok Aun told The Straits Times.
"Teenagers have mobile games and video games at home so arcades have become less popular with them," said Mr Tan.
In Mr Zhen's case, he was first introduced to the game when he saw others in his age group playing it.
He insists that he does not skive from his job and goes to the arcade only in between deliveries.
He said: "To be honest, this isn't a very fun game. I'm just here to idle the time away."
WHAT IS FISH HUNTER?
Fish hunting games belong in the shoot-'em-up genre of video games, in which players try to catch various types of fish by casting nets or firing bullets at them.
While players refer to it as Fish Hunter, it has numerous variants and names, depending on the manufacturer.
Players have to buy credits from the arcade counter.
They use a joystick and buttons to point and fire a turreted gun, with each shot costing a certain amount of credits.
Players also have the option to upgrade to higher-powered shots.
These will cost more credits.
If a fish is captured, players will be rewarded with a certain amount of credits, depending on its value.
Gold creatures or "bosses" are worth a lot of credits but can take many hits to take down.
When the player stops playing, he can choose to redeem the credits for vouchers, toys or snacks at the arcade counter.
This article by The New Paper was published in MyPaper, a free, bilingual newspaper published by Singapore Press Holdings.