我的翻译是
The past several years have witnessed a fact that aging population has became a global phenomenon.It's inevitable and it will become increasingly serious as time gose by,especially in developing countries.It has far-reaching impact in society and various expression.Once ignored,it will cause great loss to our society.To ensure that the aged population develops sustainably,our country,blahblahblah,especially the elder themselves,ought to make concerted effort.
如果四级水平的话你翻译的还行,只是有些词语有些累赘.大的问题就是if ignored那一句逻辑关系不对,被忽视的是老龄化现象,而不是损失.