Well my mother came in blushing one day.. all red faced and the like, told me that she wanted me to go with her to get birth control, and I didn't ease her "suspicions" by telling her that I wasn't sexually active until I found out that I was allergic to birth control and she started worrying that I'll be pregnant.. haha. She never had the talk with me though, I don't think she could have gotten through the whole thing. She gave me pamphlets on Safe Sex practices though.
I though have given two "Talks," to my brother and to my sister. My brother being 13. I was scared giving him "the talk" because I'm female frankly and didn't want to discuss it with him, because I doubt I could really cement every topic correctly. I did it anyway.. we discussed like everything. Condoms, being responsible for your own safety first, (like bringing the condom not expecting someone else to). I told him that Sex was more than just a physical act that its something that shouldn't be dominate in any relationship. I told him that he'll likely grow, his voice will crack and change, that he'll become more hairy. Of course at thirteen he was already starting some of that, so. The Health Class in high school covers Puberty so.
I'm not surprised that you told your oldest son about sex at the age of 10. It seems that kids are exposed to more now than, I know I was. I mean my sister at age 9 had already seen a condom because someone's older sister had left hers out and her friend stole them.
With my sister it was a lot easier. I could easier tell her what her body will be doing and I had help by taking her to a gynecologist.
I talked about Homosexuality with them as well so I covered all the bases I think.. If I didn't I hope they come to me with questions when they need to.
I just really hate that my mother can't be more into the parenting? lol... but someone needs to do it. I think puberty discussions and sex talks are important.