Is it only possible to look at solar systems with stars at least as old as ours to be able to find intelligent life? Assuming the speed it takes to development intelligent life is the same in all solar systems, would we need to look at exoplanets with stars as old or older than ours to find intelligent life? A young star would be assumed to have been surrounded by planets that are relatively new and haven’t had time to develop intelligent life. Visiting those planets with young stars relative to the sun would most likely only give us planets with prehistoric life.
Assuming the speed it takes to development intelligent life is the same in all solar systems,


We don't know if this is true.  

We don't know if:


Life has started on more than one planet in the Universe.
How long, on average, it takes for life to start.
Whether life normally evolves past the "bacterial slime" stage to form complex multicellular life, and how long this takes.
Whether multicellular life normally develops intelligence, and how long this takes.
How long intelligent life survives, on average.


So we don't know what time it takes to develop intelligent life. However, planets are the same age as their stars, so it is reasonable to suppose that older stars are more likely to harbour intelligent life.  

Moreover, visiting any extrasolar planets is too hard with current technology. Stars are just too far away.