It’s not absolutely impossible to get corporate sponsorship at such a young age, however, you’d have to be a pretty phenomenal athlete. Even Freddy Adu wasn’t sponsored by a company that size at age 14. In general, most 14 year olds won’t receive individual corporate sponsorship.
It is, however, still possible that your team or organization could be sponsored by a large corporation.
Every corporation has a different process. If you have some companies in mind, your coach or team administrator should contact the regional headquarters to find out their specific process. It usually begins with an application giving details about the team, number of players, awards and major wins, etc.
In either case, much of getting sponsored is about networking and knowing the right people. That’s just the way it goes.
If you’re a pretty good player, or if you’re at least motivated to go out and give it a try, you and your parents might try talking to local businesses like sporting goods stores to see if they will sponsor you and perhaps provide you with the things you would have wanted from adidas.
Be careful though. Sponsorship through a team is usually ok, but if you get sponsored individually (even by a local company), you will risk losing your amateur status, and that could keep you from playing in high school, college, and a lot of youth leagues.