If you want to become an advertising copywriter, it's certainly possible as long as you have both the needed skills and the ability to persevere in your dream career. The ability to express yourself not only creatively but persuasively through writing is crucial. Copywriters need an original, imaginative mind as well as critical thinking skills to understand the needs and desires of their target audience. Career possibilities for an advertising copywriter include working in an ad agency or department as well as freelancing for many clients. There is a great deal of competition for full-time jobs in the industry, so if you want to become an advertising copywriter you'll have to find out what potential employers in your area want and market yourself as their ideal employee.
Advertising agencies now typically want their copywriters to have at least a bachelor's degree, but you may be able to be hired with less education if you can impress them with your book. In advertising, a book refers to the portfolio of ad work that you've done. The book may be a bound paper type of portfolio with print ads or an online one with advertisements you've written in different mediums.
If you have no experience as an advertising copywriter writing ads for pay, try to get an online freelance copywriting assignment or two that you can also use for references on your resume. The pay isn't likely to be high, but if it will allow you to have a good reference and work sample for your book, it can be worth doing. If you have trouble getting any kind of paid ad copywriting experience but still hope to become an advertising copywriter, you should create mock ads for existing products to demonstrate your ability and to show your desire to be in the field.
Above all, advertising agencies or ad departments within businesses look for talent. It takes a lot of perseverance to keep making the rounds and getting your book out there. Eventually, if you have the talent and don't give up your dream to become an advertising copywriter, you're likely to get hired as an intern or in a junior position. Junior copywriters often have some copywriting experience, but it may not be necessary. The best way to get hired is to be politely persistent and keep studying ads and trying to get some freelance copywriting gigs to add to your portfolio.
Keep studying all of the ads you can; try to find out what makes the good ones work and the bad ones fail. Try to determine the target consumers of different products and services. If you can't complete a bachelor's degree, at least try to take an advertising or marketing course or two. If you are planning on completing a degree in a subject other than advertising, adding courses in psychology, English and communication may be a good alternative. The main thing is to market the skills you've learned from whatever education and training you do have when you're applying for a job to become an advertising copywriter.