can you aim and fire in one turn

Why wouldn't you? If I recall (no book with me), Aim is a maneuver that adds a boost die, and firing (attacking) is an action. Characters get 1 maneuver and 1 action per turn. Actions can be converted/downgraded into maneuvers if desired, or a character can suffer strain to take an extra maneuver. You can only take 2 maneuvers a turn max per turn. As long as you are armed at the start of the turn, and your target is within range of your equipped weapon, you can aim and attack.

I'm nearly certain its possible to aim twice (two boost die) and attack if you really want to. You're just eating strain.

can you aim and fire in one turn

Yes.

Mechanically: yes. Aim is a maneuver, shoot is an action, so you can do both in one round. If you can take a second maneuver (like by spending 2 strain) you can aim twice before you fire, getting a double bonus.

Narratively: Yes, remember this system doesn't lock turns to a set time. So a round can be (any usually is) about a minute or so, with a single attack roll representative of several shots, or one, or whatever the narrative require. Bottom line though, in the game these enough time in a round to aim and fire.

I highly recommend using the Aim maneuver whenever possible. It's basically how anyone can be a decent shot. You made a Politico with Agility 1 and no combat skills? Grab a rifle, take cover, and Aim. 1 Green and 2 Blue is better than 2 Green, almost as good as 3 Green. You won't trigger a lot of fancy abilities, and you'll have a tough time with tricky shots, but you can certainly help whittle down those Stormtrooper squads a bit.

Of course, if there's something else you could doing with your abilities, (scathing tirade, hotwiring a speeder), do that instead. Just remember that Aim makes combat a viable option. Which makes sense. Shooting a rifle isn't that hard, if you can take your time and line up your shot.