if you are young, you can take more risk, hence put your investment in equity.
if you are old, you should keep your capital in safer vehicle like bond etc.
But one important strategy they miss out is ... the dynamic of personal finance portfolio.
Says you are 25 years old, you will need a sum of money at 35 years old. Hence you can invest into equity. However, you must learn something about the equity market you are entering into. For example, you know that for every 10 years in your equity market, there will be a peak and a bottom. So perhaps by 3-4 years before your maturity date, ie. 31-32 years old. You should start considering withdrawing your equity investment and keep them in a money market or bond fund. This will preserve your capital and secure you from unexpected last minute change, ie. a sudden equity collapse.
age 25 : 90% equity, 10% bondage 27 : 80% equity, 20% bondage 32 : 40% equity, 60% bondage 34 : 10% equity, 90% bond
Keeping a non dynamic portfolio expose you to risk the whole time. If bad luck hits you, you may lost all your 9 years of earning in the 10th year. So one must keep ones personal finance portfolio dynamic.