Kinsey, Alfred, Pomeroy Wardell B., & Martin Clyde E.; Kinsey Report -- excerpted entries on homosexuality; Excerpts from a book
Excerpts from Kinsey et al's Sexual Behavior in the Human Male:
[Chapter 7: Age and Sexual Outlet, pp. 259-261] Homosexual activity and age.
[Chapter 8: Marital Status and Sexual Outlet, pp. 259-261]
[Chapter 10: Social Level and Sexual Outlet] - [sub-heading: Incidences and Frequencies of Sexual Outlet, pp. 357-362] & [sub-heading: Patterns of Behavior, pp. 383-384]
[Chapter 12: Rural-Urban Background and Sexual Outlet, pp. 455-459]

Kinsey, Alfred, Pomeroy Wardell B., & Martin Clyde E.; Sexual Behavior in the Human Male (Chapter 21 - HOMOSEXUAL OUTLET); 0-1
[...] Homosexual contacts account, therefore, for a rather small but still significant portion of the total outlet of the human male. [...]
If homosexual activity persists on as large a scale as it does, in the face of the very considerable public sentiment against it and in spite of the severity of the penalties that our Anglo-American culture has placed upon it through the centuries, there seems some reason for believing that such activity would appear in the histories of a much larger portion of the population if there were no social restraints.
The homosexual has been a significant part of human sexual activity ever since the dawn of history, primarily because it is an expression of capacities that are basic in the human animal.
Kinsey, Alfred; Sexual Behavior in the Human Male (1948) - chapter 5 - Early Sexual Growth and Activity; 35 pp, 157 - 192
Chapter five, here presented as a .PDF file, is devoted to early sexual growth and activity and first sets out to define erotic arousal and orgasm, noting the variation in pattern of orgastic response in individuals.
One significant finding was that more than 99% of these boys adopted a regular routine of sexual activity after the initial experience of ejaculation.