being teen, mature, and old

Once my friend said today. Life is funny. Then I asked him, "why?"

He said three phases you may pass in this life. Being teen, mature, and old will teach you that we always will loose some part to have a full life (energy, money, and time). I am not talking this happens to everybody because for myself I do not accept it and I do not feel like being the majority who experience this funny things.

As teenager, one has the energy and the time to do things, but usually he or she has less money.
As the mature person, one has the energy and the money from the salary and earnings, but consequently he or she has less time.
As the old person, one has the money and the time to do things, but usually he or she has less energy because of tired muscles.

From my perspective this is the paradox of life and that's why it is not funny but it is beautiful.