No, this is not true. Missionary service is purely voluntary. My parents paid for most of my mission and my undergraduate education. I paid for my graduate education by working at various jobs and by earning scholarships. The Church did not pay for any of it. The reason most missionaries are young is because this is the best time of life to take two years out to serve a mission. At this age, people are usually at their healthiest and don't have other responsibilities to tie them down. Earlier in life they are usually not mature enough and later in life they will have the responsibilities of earning a living for themselves and/or their families. It is also not true that all of our missionaries are young adults. Many missionaries are retired members who no longer have to worry about dependent children and careers. These missionaries can serve in a much broader range of missions. These mission can include proselyting, education, welfare projects, disaster relief, and many others. Again, all of these are also purely voluntary. We do these things because we love our fellow men, not to get some personal gain. What you may have heard about is a completely separate program that the Church has. This is a program call the Perpetual Education Fund. This program lends money to people economically disadvantaged members, who live in under developed parts of the world, to help them get an education so that they can get better jobs. These people are then expected to pay the money back over time when they do start working. The money they pay back then goes to some one else to help him/her get an education and so on. Again, this does not amount to a free education because the recipient of the money is expected to pay it back, but it helps disadvantaged people get educations that they might not otherwise have been able to afford. This helps them to be more prosperous in their own lives and to achieve the dreams that might otherwise have been denied to them. One other thing to note about the Perpetual Education Fund, 100% of the money donated to it and gathered in repayments goes to financing educations. None of it goes to administrative costs. (This is something that is true of all of the money that is given to the Church's various welfare projects.)