Saving enough for 100?

Saving money and investing it in the stock market. I like index funds. Over many decades it compounds and exponentially grow. If someone think they can’t stomach the volatility (-60% at times) I’d add in some bonds too, or if nearing retirement. Vanguard LifeStrategy funds might be good.
For wealthy investors I’d recommend independent financial advisors. Those that get paid by the hour and don’t push high fee products. Fees are terrible for investments. Not financial advice.