Sandra Bullock is 50 in 2014 but you'd never know it by looking at her. This style will be the most difficult to copy with a wig just because it's longer.
One subtle Sandra signature is that she parts her hair in the middle most of the time. Sometimes she has a very deep side part for an Old Hollywood look. When it's parted in the middle she doesn't part it all the way back.
There have been stages where she's had a lot of hair coloring and highlights but she seems to have simplified. She will occasionally have a few highlights in the front but now she goes more for a solid shade. She's taken out a lot of the red from her hair and gone for a more solid (but still beautiful) color.
Styling your hair like Sandra's is going to be fairly simple. She does occasionally do the beach waves thing for casual wear. However, more often she just has very sleek, very long, straight hair. She either wears it over her shoulder, back in a ponytail, or straight down her back. Why is this different from your straight hair? It has a lot of shine to it and it's so straight that it looks intentional instead of like she just woke up.
Sandra really broke the rule that we usually think about age; that your hair needs to go lighter and shorter as you age. While you may not be lucky enough to be able to do this naturally look for quality extensions or a wig to achieve this look.