The needs of the same human being may differ at different stages of life. Can there be one Dharma for all stages?
Yes there can be one Dhamma for all.
The Dhamma taught by the Buddhas is timeless and does not change. These rare beings discover the path for themselves, they discover an ancient path, after which they teach it to other beings.
The Dhamma is always the same. The Four Noble Truths do not change whether one is 5, 30 or 90 years old.
There is though, different approaches to the Dhamma, depending on what age a human being has.
If one is 5 years old, then a more simple and fantastic approach might be used. For example one uses in greater deal the stories from the Jatakas, to illustrate the different path factors such as ethical conduct.
One might also approach it from a school teachers angle as Crab Bucket has done. He used clay to form dhamma wheels and drawings of the Buddha surrounded by animals. Ven. Yuttadhammo has made a video-series on how to do Metta meditation for kids. In the videos he speak very slowly, calmly and simply. It works really well for kids.
So in other words. If one is pretty young in age then the complexity of the Dhamma, such as the technicalities of the Abhidhamma might not be the best approach:)
If one is 30 or 90 years old, there are many different approaches. The best way to explain this, is to look at the different affiliations of Buddhism and then find an affiliation or several affiliations, that fits ones own understanding of the Dhamma. In the end, they all lead to the same goal, Liberation.
Ultimately, to understand the Dhamma, one has to practice meditation. In the meditation one will truly understand that the Dhamma is timeless and always the same for all ages and stages.