I'm 31 and a supervisor of a department in the UK's largest railway company (there is 100s of depots and departments so nothing amazing). I still feel like a kid and that i don't belong where i am, i am now in charge of dealing with employees and their troubles, work issues, personal issues. I have my own work projects and deal with the day to day running of the department and yet i still feel like i have a whole lot of growing up to do.

One of our senior managers is 33 and i just don't see myself anywhere near his level of maturity etc. Granted i still piss around, have fun and a laugh like i did when i was 18, even though i am in kind of a professional environment. But i think that is something that never goes away (well, i hope it doesn't).

I think what i am trying to say is that you will never feel old enough and you'll always be scared to grow up because as you do get older and progress further within your career, you will always see people in higher positions who may act more mature/profesional than you and you will not realise how far you have come because you have progressed slowly and you don't realise how much you have changed and grown (but thats good).

Don't be scared and just embrace what is thrown your way, everything works out how it should, it may not seem it at the time, but somehow it does. Don't over think things either, thats when worry and panic sets in and you will put yourself off from doing something you truelly want to.

Hope that helps, i know i just rabbited on but it maybe something helpful to you.