Start now. The absolute biggest advantage in growing an investment base is time. In a lot of ways it’s more useful than a high income, because a high income typically brings a higher expected living standard.
But with time… well then you can see the wonders of exponential growth. If you make an investment that nets 8% and cash out ten years later then you’ll end up with a bit over double what you started with. Cash out after 30 years and you’ll have 10 times what you started with.
And on top of that time gives you the luxury of being able to ride out the fluctuations. If you invest needing that money in five or ten years then you’ve got to be very conservative, putting it in secure but low return options like interest bearing accounts. But if you have the luxury of looking 30 years ahead then you can accept short and medium term volatility – over 30 years the stock market is the most likely to get you your best return, but the price of this is that you have to accept wild variations in the short term.