Retirement...is it achievable with the cost of living these days? Asking on behalf of someone who will never touch $100k per year with their career. Is investing my only hope to do this?

So I see a lot of posts with people asking about retirement investment moves and as I'm reading the posts, the majority are already sitting on $500k, $1.5 million or more. Great! I'm happy for them but to the average person who doesn't make over $100k a year, how can one achieve this? It's never too late to start investing, I fully understand the concept. Are ETFs the answer? I read something that said at the age of 40, I would need to invest $4k a month to reach retirement and live comfortably. If I put $4k a month into investing I'd be living on the street and the family would go hungry. Is the move to gamble on a penny stock? I'm just genuinely curious to see what others would do. We can't turn back the clock and start investing young. What's the play?

Thank you