If what you want to say is something like "Japan is seeing an aging population", then there is no better term to say it than that (there are worse ways of saying it though). If you are saying "I am getting old", in a sort of funny way, you can say "I am maturing". See the difference? In addition, I don't think you can really type it as "ageing". It seems obviously wrong to me. If someone could please tell me in which part of the English speaking world you can spell it as "ageing" and seen as correct, please let me know. I am serious.

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Note added at 12 hrs 12 mins (2004-06-24 21:40:58 GMT)
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Okay. Thanks to jyuan_us and some others. I learned quite a bit today. And yes, ageing is also right. The asker\'s question is seen correctly under \"Japanese SHIFT-JIS\" encoding.

You can read my answer in Traditional Chinese Big5 encoding. Thanks. example: 擔杮涍鉙绨擖堦屄崅陻壔揑幮橉

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Note added at 12 hrs 30 mins (2004-06-24 21:58:35 GMT)
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I am sorry. I just realized encoding is not based on \"what input encoding I use\", but what encoding view I selected for the browser when I typed it. So my answer can be viewed using \"Japanese SHIFT_JIS\" encoding. Cheers.

老化is the best Chinese term for ageing or aging，if you want express the meaning of "The process of growing old" but aging can also express the meaning of 成熟的过程(The process of growing maturing ). So it just depends your context.
Please use Chinese coding to avoid confusion, if you want answers in Chinese :)
老年means senility.

在北方口语中，~=上年纪了

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Note added at 11 hrs 45 mins (2004-06-24 21:13:56 GMT)
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If it is about a population, 老龄人口

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Note added at 12 hrs 8 mins (2004-06-24 21:36:57 GMT)
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老化 is in most cases a verb, e. g. 人口老化.




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Note added at 16 hrs 10 mins (2004-06-25 01:39:02 GMT)
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I think this is used only to describe a group. 而且专指进入老年那一段. 作为一个动态词， 不可能有清晰的年龄段划分。“进入老龄(年)期\" should sufficiently convey its meaning.

\"老化\"有些微的Negative connotation.

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Note added at 16 hrs 51 mins (2004-06-25 02:20:19 GMT)
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“人口老龄化” 倒是很常见。