You can start later than age 62, but once you start you have 10 calendar years to make all your withdrawals. If you don't withdraw everything within the 10th calendar year, your entire remaining SRS account balance is deemed withdrawn, in full, for Singapore income tax purposes. And you owe/pay income tax accordingly....
....With one exception. If you buy a fully SRS qualified single premium life annuity from Manulife, the only annuity provider currently offering such a product, then the payouts from that qualified life annuity can run beyond the 10 calendar year limit. The premium reduces your SRS balance and is not treated as a withdrawal, and the payouts are factored into the tax calculation in each of their calendar years -- 11th, 12th, 15th, 18th, whatever, as long as you live. If the annuity payout is $40,000 or less per calendar year, and if you have no other taxable income, then your Singapore income tax should be zero.