SS lists the most popular male names in the US over the last 100 years as James (4.7M), John (4.5M), Robert (4.5M), and Michael (4.3M).[1]
Using standard US mortality data, Wolfram Alpha reports estimates of 3.853M and 3.26M for Michael and John respectively, currently alive in the US.[2][3]
[1]: https://www.ssa.gov/oact/babynames/decades/century.html