Certain vaccinations have a time frame. The rotavirus vaccine is not offered to children older than six months of age, because after six months rotavirus is not as dangerous. The pneumococcal vaccine is not given after the age of 2 because after this age the risks of pneumococcal sepsis reduces considerably. Before the age of 4-5, most of the vaccines need to be given as courses of 2-4 doses to achieve a good immune response, because the immune system is immature; giving vaccines after this age may mean that only one dose needs to be given to achieve a good immune response.

In a previous thread, I posted my "ideal" immunisation schedule: you can find it here. Doing your own research is really important, though; you may find you have different priorities or concerns than my own. I think every parent needs to make their own informed decision about immunisation, and that decision should be respected.