He isn't too young for time out, but I prefer to use time out for more serious infractions -- hitting, biting, a chance to cool down during a tantrum, etc.
Throwing is definitely an irritating phase, but I don't think that time out is the best solution. Instead, try a combo of redirection, removal of him (or the toy) from the situation, and ignoring.
Remember that kids throw things to learn what happens when they do. Consider it a science experiment about gravity. ;-)
If he's throwing something that isn't harmful to him or others (balls, stuffed animals, even the fridge letters unless you deem that harmful), just let it be. I promise that this phase will pass.
If he throws something that you don't want him to throw (silverware, maybe the fridge letters), tell him that no, he can't throw that, but he can throw a ball instead. Then, take him outside or to the living room (or wherever he plays), and give him a ball. When he throws the ball, give him tons of positive reinforcement.
If he's very persistent about throwing whatever you don't want him to throw, then put it away until you think he's ready to try safely playing with it again (can be an hour, a day, a week, a month). If necessary, remove him from the situation -- similar to a time out, but without trying to enforce a specific naughty chair. Just move him to another room, and get him playing in there, keeping him away from whatever he wasn't supposed to throw.
As much as possible, be matter-of-fact, and don't make a big deal about it.
I have a 19-month-old myself (in addition to a 5- and 4-year-old), and we've been through this many times. This, too, shall pass. :-)