Age itself does not stop anyone from investing in Bitcoin or from building more cash flow. What really matters is whether someone has discretionary income and the discipline to keep stacking without touching it for everyday bills. As you said, expenses will always be there no matter our age, so the real solution is having other income streams to support those expenses. That way, whatever goes into Bitcoin remains long term. Salaries or main income can serve as the foundation, but multiple income sources give extra room to increase discretionary income and keep the investment secure.
You must not have multiple sources of income before you can comfortably invest in Bitcoin, what you need is a good source of income that can cover your basic needs and allow you have enough discretionary income from where you will invest part into Bitcoin and part of it kept as emergency funds. This idea of having multiple sources of income have made more people spread their money and energy into things they should have avoid to focus on things that will help them just because they want to create many streams of income. If you have a good business that is fetching you enough money, you can use part of your profits to start building your Building your Bitcoin portfolio. The focus is to have discretionary income and emergency funds to protect the investment from being sold when it was not planned.