Student aid is not only for the young. Thousands of adults, many of them with families, are going to college today -- and relying on an assortment of student-aid programs to get them through.

One out of every five adults is now enrolled in some sort of postsecondary educational or training course, according to The College Board. One-third of all college students are more than 25 years old, compared with one-fourth just eight years ago. Many are housewives returning to the work force; others are working trying to improve their knowledge and skills, or people changing careers.

A good many more adults would probably be in school if they could figure out how to afford it. The College Board has this advice for adults who want to add to their education but cannot do it without financial help:

Find out what your company will pay for. Many companies have excellent free-tuition programs for employes and, sometimes, their spouses. Most programs require that the courses be related to your jobs, but some will finance unrelated courses. A good many people get full college degrees on company funds and even advanced degrees, such as a Masters in Business Administration.

Write to the financial-aid offices of the schools or colleges you hope to attend. Even better, pay them a personal visit.

A school's aid office is the funnel through which all the money flows. You'll have to fill in a long form disclosing your income and assests (and, if you're married, those of your spouse). The school will also ask about your overall financial situation, such as whether you have any children, whether yor're supporting a parent or whether you have to pay regular medical bills for a disabled or chronically ill child.

Mail the financial aid application along with your application for admittance to the school. If you wait until after you're accepted and then ask for aid, all the funds may already be alllocated.

A student-aid committee decides, based on your financial disclosure form, how much you ought to be able to pay toward your own education. Your're then made an offer to cover the rest of the cost -- so much in flat grants that need not to be paid back, so much in salary from a campus job, so much from student loans.

Middle-income students often feel that they're forced to pay more of their own money that they can afford. (Low-income students, by contract, tend to expect less, hence are often surprised at larger grants that they foresaw.) Sometimes you can improve the offer by visiting the aid officer in person and showing him that your financial position is actually tighter than the college assumed.

It's important for adults to apply to more than one school, because student-aid policies vary so widely. Some colleges, for example, give less to adults than to younger people. Some give aid only to full-time students. Some exclude graduate students. One school may make you a generous offer for half-time study while another may expect you to borrow most of the money.

Always apply to at least one school within your own state. Each state has special aid programs, usually limited to residents attending state schools.

Don't forget tax savings. If you itemize deductions, remain employed and take courses that maintain or improve your present job skills, you can generally deduct the money you spend on tuition, books, transportation and living expenses if away at school.

Apply for a subsidized student loan. Many banks offer student loans that cost you nothing at all -- except, perhaps, a small application fee -- while you're in school. When you leave, you have up to ten years to repay at only 7 percent interest. Not all banks make these loans. If you are having trouble finding a lender, ask the school financial aid office for suggestions. Undergraduates may borrow up to $2,500 a year, and up to $7,500 during their undergraduate career.

Adults also may apply for Basio Educational Opportunity grants, offered by the federal government. These grants are based entirely on need, without regard to past academic performance. Application forms are available at any high school guidance office or college financial-aid office.