<< and there hasnt been a scientific explanation why things get old and cells stop regenerating after certain time. >>
Actually there has been a explanation offered, which seems to be correct but is not for certain yet. If I remember correctly, on the ends of chromosomes are sections called telomeres, which "protect" the DNA. As cells divide these telomeres get shorter and shorter over time. When the telomeres are gone, poof, the cell is kaput.