La Tomatina

Hello!
We are 30 year old couple planning to travel to Valencia with my husband for holiday. I am interested to know some information about La Tomatina. How is the afterparty, Is it only a tourist thing or are there also local people?  and is there only young people about 20-years old in the afterparty?  We are thinking is it better to go afterparty in Chiva or to go party in Valencia after the festival La Tomatima?

maybe ask this question on a vacation travel form?