Sheet1
A       B       C       D           E
name    date    unit_1  unit_2      unit_3
John    1-2-3   3       9           7
John    2-2-3   9       13          16
Maria   9-10-4  10      8           7
Maria   13-5-4  6       3           7
Maria   9-8-7   8       7           3

Row #2
A   = INDIRECT(CONCATENATE("Sheet1!A",B2)
B   = IF(ROW()=2;2;C1+1)
C   = A2+MATCH(TRUE,INDIRECT(CONCATENATE("Sheet1!A",B2,":","A",B2+10))<>A2)-1
D   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!C",B2,":","C",C2)))
E   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!D",B2,":","D",C2)))
F   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!E",B2,":","E",C2)))
G   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!F",B2,":","F",C2)))
H   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!G",B2,":","G",C2)))
I   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!H",B2,":","H",C2)))
J   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!I",B2,":","I",C2)))
K   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!J",B2,":","J",C2)))
L   = AVERAGE(INDIRECT(CONCATENATE("Sheet1!K",B2,":","K",C2)))