Participating in the 'market' is an education. Taken seriously, it will lead to a much better understanding of how the World works.
I do not think it matters where or how you begin, but it does matter what your attitude is. An 18 year old is still a baby. In another dozen years they might start to know themselves. An 18 year old is highly unlikely to understand the motives and drives of people 3 times their age ... but most of the people driving the businesses listed on the ASX are that vintage. Those businesses which fail [and take your money with them] often do so because of the faulty attitudes embodied in the management.
Understanding your own values is important. An unethical person can seldom recognize the lack of ethics in another person. An ethical person is better equipped to know when to trust another person. Even after examining a business closely and confirming its credibility as an enterprise, trust remains a major factor. It takes courage to trust others.
Reliably understanding why a company might be a superior investment [and therefore also a prospective trading opportunity] will only come from experience and insight into the major themes at work in society. Becoming actively involved in the market can only benefit a person in understanding the times they live in.
Keeping a perspective is important. The market, although it reaches into many aspects of life, is still only a facet of this World. It pays to have a healthy disregard for money.
One piece of practical advice ... do not use borrowed money to play in the market, always pay your bills first and do not sacrifice time which might be well spent with others.
