Any sperm has the potential to make you pregnant. Understand the facts:
Planned Parenthood
http://www.plannedparenthood.org/info-for-teens/pregnancy/am-pregnant-33831.asp
so a immature sperm can make someone pregnant..?
I have no idea if you're asking about sperm from an immature or young male or if you're asking about one individual sperm that is not fully developed. What makes it sperm is it's ability to initiate a pregnancy.