Working in any startup is always going to be risky, by definition, regardless of location. If there was not a high degree of risk, it wouldn't be a startup, it would be an established business. It sounds to me like this could be a great opportunity though.
if you want to be in top of IT industry you just need to be in SF
I don't agree with this at all. There's no denying that San Francisco is a city that is ripe with opportunity, support for startups, both socially and and financially. But there is opportunity everywhere, and there are individuals and organisations that are disrupting entire industries who are based in other cities and other countries the world over. It's complete myth that you need to relocate to SF to be have a successful technology business.
It might be useful to consider what your goal is, other than "work at the top of the IT industry". What industries are you interested in or passionate about? What kinds of people do you enjoy working with or helping? What do you hope to achieve, personally and professionally, from life? Do you aspire to work for yourself? Run a team? Have the freedom to choose which city you work from, and which hours you work? The answers to these questions may prove to be better guides for your big decisions than chasing some arbitrary "work at the top" dream.
in little more then 6 months I going to be 19 and I feel already old and like I have felling that my skills are not good enough for my age
It's a good sign that you're aware of yourself and keen to learn more. Keep a healthy balance between wanting to constantly learn, without letting it sap your confidence. Sure, you have stuff to learn. But I bet there's a ton of stuff you're really good at already. Back yourself sometimes—there's only one person who can hold you back, and that's you. So don't let that happen.
btw is true that ux alone(not ui) is only 1.5 years old?
The term "user experience" was coined by Don Norman (author of The Design of Everyday Things) in the 1990s, and the term gathered momentum as a "movement" in the mid 2000s. Before that, there were certainly practitioners taking a more holistic approach to creating digital design, although they weren't calling it "UX". Likewise, the concept of iterative design and involving users in the design process is one practised by industrial designers for years—web designers were somewhat late to the party in adopting it more widely as "best practice".
Hope that's helpful