Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:6/8
K:G
['GAB AGE', 'B d^ce def gfe dBG Bcd efg']  
X:1
L:1/8
M:6/8
K:G
 D | GAB AGE | ceg dBG | GAB AGE |{G} FDD DEF | GAB AGE | ceg dBG | EFG (A<d)c | BGG G2 :| B | 
 d^ce def | gfe dBG | Bcd efg | (g<b)g afd | (g/a/b).a gfe | dBg dBG | EFG (A<d)c | BGG G2 :|  