Lego list the age for their hero factory toys as 6-16 so 8 fits perfectly in the age bracket they say. Also legos is one of the best building sets out there. K'nex is another option depending on exactly why you were thinking LEGO in the first place.
lego and stickle bricks
Yes its like a U, they are made for kids under the age of 8.
18-25
Lego or Lego Digital Designer
The target age group for Bionicle Lego toys was ages 6-12. In November of 2009, Lego announced that Bionicle Lego toys would be discontinued after 2010.
The LEGO's mindstorms Nxt products have similar age recommendations to other Lego products, due to the possibility of ingesting pieces. The most appropriate minimum age is 10.
The Lego Batman games do not have an exact specific age which they are most suitable for but they are recommended for children who are ages eight and older.
The advised age restrictions for LEGO toys is 4 and up with parental supervision. The small pieces of LEGO can be hazardous to a small child so parental supervision is a must.
Lego
According to the official Lego website, individual Lego Spongebob toys may have different age requirements. Some are designed for children aged 5-12, others for children aged 6-12. Based on these age ranges, all Lego Spongebob toys should be appropriate for a six-year-old.
Lego Friends is generally aimed for children between 6 - 12, so the set would be appropriate for your child. You can find this information at www.amazon.com, where age ranges are listed for most Lego products.