The old school crap all the financial planners use is percentage of the bond in your portfolio is your age. If you are 60 years old , then 60% your portfolio is bond, 40% stock; if you are 70 years, then 70% bond allocation.

Modern days people don’t do that any more. There are several reasons:
1) Bond yield at 2% are still historically very low. We no longer have The old days bond can return 7% a year and provide good safety income return for retirement income. People used to just own GNMA bond fund for 7% safe return, but no longer attractive now.
2) People who already meet their basic retirement need can go more aggressive in investment. Many piggs who own rental homes fall into this category.

I would personally prefer age – 20 as my bond allocation during retirement. I can allocate 45% in bond when I turn 65.