"""
The law [UK sexual offences bill] would also prohibit encouraging a (so-called) child to take part in sexual activity. I think that everyone age 14 or above ought to take part in sex, though not indiscriminately. (Some people are ready earlier.) It is unnatural for humans to abstain from sex past puberty, and while I wouldn't try to pressure anyone to participate, I certainly encourage everyone to do so.
"""
There are more charitable interpretations, but "Stallman wants to sleep with your teenage daughter" is the less-charitable one that political opponents can continue to levy against the entire movement because the FSF won't let him go.
Without knowing more context, I interpret the quote to mean that 14-year-olds should be open to having sex with their peers (other 14-year-olds, give or take one year). Which seems like a position that is not bad enough to punish. It's a very weird thing for him to say, given that everyone knows him for being the president of the Free Software Foundation and not the Sexual Openness Foundation. He should stop commenting on this topic and focus on Free Software instead.
Who are you talking about? This is completely misleading and not what Stallman was saying.