At your age, you are not looking at making great gains, but to keep pace with inflation and possibly passing on your legacy to your heirs (this is an important consideration). If you want to pass on your wealth (if you have heirs) and your needs are not particularly luxurious, you can possibly live off dividends thrown off by the portfolio. The STI throws off roughly 3% p.a*., and the US S&P500 throws off roughly 2% p.a. (after the withholding tax, I think). You can even allocate some to form a REIT ETF portfolio that can give >4% p.a..
On the other hand, if you aren't going to leave anything behind, a 3 or 4% drawdown rate is fine. 4% is, IMO, on the aggressive side with projected economic growth, so I'd personally prefer 3%. Besides, you do get CPF payouts, so I don't think you are short on funding your retirement. Buying a Greek island is not included.
Under (conventional) portfolio theory, you should hold still some stocks even at your current age. 10 year Singapore sovereign bonds are not going to beat inflation. For the stock component, see below.
Unless you have a track record of successful stock picking, avoid that and instead simply put inside low cost passive index funds like the STI (ES3 or G3B) and probably one to cover the rest of the world (eg. IWDA or VWRL listed on London). Individual stocks can crash and never recover, but the general market (tracked by the index) will as the economy recovers.
How do you allocate b/w stocks and bonds? Warren Buffett said that when he is dead, his wife should just hold 90% stocks (in the S&P500) and 10% bonds. That is probably not acceptable for most people as they are unlikely to manage that big of a portfolio that they can still live off dividends paid out even when the market is down 50%. John (Jack) Bogle himself holds 2/3 stocks (again in the S&P500) and 1/3 bonds, though has moved a 50-50 split recently, probably due to the relatively higher valuations of US stock market. He's 88 right now with a heart transplant ~20 years ago. Note that they are only vested in the US stock market, which behaves quite differently from ours.
If you wish to use the 100-age or 110-age stock allocation rule, 50-50% is about right, and you can move downwards in stock allocation if you so wish. Of course, if you wish to leave behind more money for your heirs, maintaining 50-50 is still reasonable given your portfolio size**.
* Clearly, this depends on market conditions. You can take a look at the performance of the STI and the dividend payouts of the two index funds tracking it.
** I know Shiny may not agree with this.