Investing for retirement is always a great idea but which product is the best? : Thanks to the rocket fuel that is compound interest, it’s never too early to begin planning for your retirement. What may seem a small amount in the early days can balloon over time if you stay patient and refrain from meddling with your portfolio. But which retirement-focused product — a Lifetime ISA (LISA) or Self Invested Personal Pension (SIPP) — is best? Here’s my take. The Lifetime ISA can be opened by anyone between the ages of 18 and 39.