Were age discrepancies common in relationships at the time

What do you mean by "age discrepancy"? That their ages weren't perfectly matched? That their ages were some distance that someone considers "unsuitable" then or now?

Honest, I thought people not being grade-matched was more common than not, so it seeming odd seems odd to me. Is there an assumption that children can only "decently" relate to others their own age?

Were age discrepancies common in relationships at the time, was the behavior instigated by the draft (the line used was something to the effect of "Well you're supposed to take care of a boy in uniform"), or was the drama simply inaccurate?

A 13-year-old being romantically involved with an 18-year-old was definitely not common in the 1930s-1940s. Can you provide some more context for the situations shown in the drama/documentary, and maybe the name of the program? It seems like through the whole question you're conflating gift-giving with romance, but sewing or knitting items for soldiers was simply a home front activity to support the troops. You could make something to send to a young man you loved romantically, but you could also send care packages to friends and siblings, or as part of a group effort for the front in general.