Thirty years is an extraordinary span of fecundity for one woman.  Either the couple in Pennsylvania in 1790 is not the couple in Ohio in 1820, or the youngest boys in the 1820 census are not their sons, or Stophel had at least one additional marriage — to a younger woman.  Otherwise, I see no obstacle to the couple in Pennsylvania being the one in Ohio.

1.  Marriage Record:

2.  1790 Census Index/Images (online at Ancestry.com; Image #19 of 23; extracted by Diana Gale Matthiesen):

1790

PA

Lancaster Co.

Cocalico Twp.

p. 180

Ln. 21

Stophel Miller

3-3-4-0-0

These data indicate:

Gender and Type	Age Class	Therefore Born	Individuals Inferred
3 free white males	16 or over	in or bef. 1774	= Stophel = Son A = Son B
3 free white males	15 or under	1774-1790	= Son C = Son D = Son E
4 free white females	all ages	in or bef. 1790	= wife = Daughter A = Daughter B = Daughter C

Note that some of those listed in the household may not be members of the nuclear family, though I'm treating the household as if they were.

3.  1800

4.  1810 Census Index/Images (online at Ancestry.com):  not found.  The 1810 census of Ohio was lost (except for Washington Co.).  There is only one Stophel/Stofel MILLER indexed on this CD and he is in Montgomery Co., MD.  I don't believe he is our subject because he has no children and the woman living with him is in the next older age class.

5.  1820 Census Index/Images (online at Ancestry.com; Image #1 of 5; extracted by Diana Gale Matthiesen):

1820

OH

Highland Co.

Brush Creek Twp.

p. 32

Ln. 35

Stofel Miller

001211-00001-0-300

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	16-18	1801-1804	= Son G
1 male	19-25*	1794-1801	= Son F
1 male	26-44	1775-1794	= Son E
1 male	45 or over	in or bef. 1775	= Stophel
1 female	45 or over	in or bef. 1775	= wife?
3	persons engaged in agriculture
*In the 1820 Census, the third column is age class 16-18 and the fourth column is age class 16-25; therefore, any individual in column three is duplicated in column four.  By subtracting the number in column three from the number in column four, you can create an age class "19-25."

Stofel is mis-indexed as being on p. 32 in the town of "New Martin."  To being with, it's the town of "New Market," but Stofel is in Brush Creek Twp.  There are three other MILLERs indexed as being on p. 32 and in "New Martin," but they, too, are in Brush Twp.  One is Samuel MILLER, who is listed two lines above Stofel MILLER, who is one line above Jacob MILLER who is two lines above John MILLER.  There are three other MILLERs indexed as being in Brush Creek Twp., two of whom actually are:  Daniel MILLER, on p. 33, and Jonathan MILLER, on p. 34.  The third is Christopher MILLER, who is, indeed, on p. 35, but he is in Salem Twp., not Brush Creek Twp.