It doesn't take in to account at all those who abstained.

Abstained? You mean helped Reagan win? How'd that strategy work out?

And it doesn't list by generation just by 10-year increments.

False. Behold, arithmetic!

1980 election
Age (DOB) Range
18-21 (1962-1959) =3
22-29 (1958-1951) =7
30-44 (1950-1936) =14
45-59 (1935-1921) =14
60+ (1920-past)

1984 election
Age (DOB) Range
18-24 (1966-1960) =6
25-29 (1959-1955) =4
30-49 (1954-1935) =19
50-64 (1934-1920) =14
65+ (1919-past)

What they lack is a neat cutoff at 1945.

And generations don't fall into neat 10-year increments.

No one is doing that.

Wikipedia:

The generation is often defined as people born from 1946 to 1964 during the mid-20th-century baby boom that followed the end of World War II.

More arithmetic! 1964-1946=18

At that point in time boomers were anywhere from 20 to 35.

1945-1960. Sure. Seems a breath away from a neat ten year increment, but sure.