That is a great question and somewhat difficult to give a definitive answer. Yes and No.
You can often tell by the short choppy gobble of a jake, but bear in mind they sometimes gobble as hard and complete as a mature bird. The other thing I try to look for is the development of the waddles. Very often a jake's waddles will not have the larger "bulbous" appearance of any gobbler over two. But again, it's not always the case. Also the red in a jake's head is sometimes not nearly as obvious as that of an adult bird. Often you can simply tell by "build" and stature of a jake. They are often going to be very thin and dainty in apperance. If he is close enough but not in strut you can see that his tail feathers will still unevenly stack, giving away his adolescence. If you can catch at look at his spurs, that will as well will give his age away. Anything over 3/4" would let you know he was mature.
Notice the photo I pasted of the jake. All the attributes I mentioned are there. The uneven stacking of the tail feathers are a little harder to see but it's there. All this being said even if I did notice any of the characteristics mentioned I would not pull the trigger until I could WITHOUT A DOUBT identify him. If you are unsure I would pass