The Census of course has data on such things over the decades.
For all people age 25 or older the percent who finish high school and obtain a bachelors for each decade are as follows :
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Clearly over time people are obtaining higher level of education. Just about the same % of people in 2000 have Bachelors as the % who had High School diplomas back in 1940.
The Census also breaks the % figures down by age group. Here is the data for the different age groups for the % of people with Bachelors degrees:
| Age | 1940 | 1950 | 1960 | 1970 | 1980 | 1990 | 2000 |
| .25 years and over | 4.6 | 6.2 | 7.7 | 10.7 | 16.2 | 20.3 | 24.4 |
| ..25 to 29 years | 5.9 | 7.7 | 11.1 | 16.3 | 22.1 | 22.1 | 27.2 |
| ..30 to 34 years | 6.3 | 7.4 | 10.9 | 14.4 | 24.6 | 23.4 | 27.9 |
| ..35 to 39 years | 5.5 | 7.2 | 9.5 | 13.8 | 21.2 | 26.4 | 25.9 |
| ..40 to 44 years | 4.7 | 7.4 | 8.1 | 12.4 | 17.5 | 27.7 | 25.9 |
| ..45 to 49 years | 4.2 | 6.5 | 7.4 | 10.5 | 16.0 | 23.5 | 28.5 |
| ..50 to 54 years | 3.8 | 5.6 | 7.3 | 8.8 | 13.9 | 19.4 | 29.1 |
| ..55 to 59 years | 3.4 | 4.9 | 6.2 | 8.1 | 11.8 | 17.2 | 24.6 |
| ..60 to 64 years | 3.3 | 4.3 | 5.0 | 7.9 | 10.0 | 14.9 | 20.3 |
| ..65 to 69 years | 2.9 | 3.7 | 4.1 | 6.6 | 9.0 | 12.5 | 18.3 |
| ..70 to 74 years | 2.6 | 3.6 | 3.6 | 5.5 | 9.0 | 10.6 | 16.2 |
| ..75 years and over | 2.3 | 3.3 | 3.2 | 4.6 | 7.2 | 9.5 | 13.3 |
You can see the peak as of 2000 was actually among the people age 50-54. This surprises me a little bit as I was assuming that the % of people with degrees would be lower with age in general. However if you give them a few more years the 20-30 year old group may start to take the lead.
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