It might sound surprising to some, but you should Start early if you want to build a big corpus for your retirement since in your 20s even though your earning might be little, but you have very less responsibilities as well. So this is the time whatever little you can save, you should try your best as not only starting early will give you the Time needed to build a big corpus but the power of compounding will come into effect and your little but regular savings at an early age, could grow to a big amount over time.
How to invest at 25?
Assuming you are salaried, you should Contribute to the 401(k) or the 403(b) plan offered by your employer and make sure the amount is the maximum you can, since your employer will contribute an equal amount, so why lose out on that?
Mutual funds can be great option too, you can regularly invest in some top mutual funds for the long term. Remember they are linked to market volatility so any money you invest in mutual funds, must be for the long term(at least 5 years or more).
You don’t really need to invest in life insurance since you don’t have dependents at this age who are financially dependent on you.