The best time to start a pension plan is as soon as you can afford to do so, without over-committing yourself. The reason for this is simple – the earlier you start your pension plan, the earlier you can afford to choose to retire and/or the more money you will have in retirement, because it’s been invested and growing for a longer period of time.
Don’t wait until you’re older to start planning for when you’re older – start as soon as you can, even if you’re starting with a small monthly amount. You can always save more in future as your income grows – and getting into good savings habits as soon as possible will make you significantly wealthier over time :-)