You might be thinking of rantallion, which sounds similar to your suggestion of rapscallion.
Wiktionary defines rantallion as a person whose scrotum is longer than his penis:
A person whose penis is insufficiently long, in its 'relaxed' mode, to exceed the length of the scrotum
The problem with 'ripe', 'mature', 'fully-grown' and similar terms is that some produce is picked before it is ripe (mature, fully-grown, etc.), and some produce is picked after it is ripe. This is true not only for contemporary agriculture, in a millieu when techniques for ripening already-harvested produce have been refined and extended to accommodate the transportation needs of a world-wide market; it is also true of agriculture historically.
This, the harvest of unripe, immature produce (or the converse, overripe produce), is as true of grain as it is of many other types of produce. Here's an example of both the historical and contemporary cases:
Way, way back — as in, pre-biblical back — in time. Try the ancient grain called, variously, freekeh, frikh, farik or freek. It's actually unripe durum wheat, harvested green and then burned to rid it of its husk. The burning imbues the grain with a slight smoky flavor.
(From "The new (ancient) grain", Chicago Tribune, July 31, 2013. Emphasis mine.)
The term 'harvest-ready' is commonly used in modern agriculture to preserve the distinction between produce that is ripe and produce that is ready to harvest, whether or not the produce is ripe.
'Harvest-ready' means just what would be supposed from the two words compounded:
ready to harvest.
That the compound 'harvest-ready' is in common use (although not readily found in dictionaries) is evidenced by the approximately 167 million hits the exact term search (+harvest-ready) produces in Google.
Best Answer
To be inclined to:
(M -W)