You are never too old to start playing and enjoying an instrument..
Make sure you really want to. Learning any instrument isn't easy and if you're not committed you'll give up halfway and will have wasted your money and time.
Never Rush. Start playing slowly and in beat. You can play that riff/lick fast only if you can play that slowly with proper timming.
Make sure your notes sound clear. There is no point in playing a solo if yur notes are not clear. Initially you might feel little pain at your fingertips but remeber " No Pain No Gain"
There are no shortcuts to learning guitar. It can take years to learn to play properly. Never Give Up !
Learnig Sheet Music is not that important. It depends on you whether you want to learn sheet music. Many artists have accepted that they no idea about sheet music.
COVER. Initally you can try to cover songs by other bands but remember your own composition is the only factor that will differentiate you from others. Everyone can go to YouTube and learn songs tabs by tabs. Your Original Composition will show your creativity and talent.
Never miss live performance. Whenever you get n opportunity just get up on stage and sing your song loudly and proudly. Never be over confident - a little stage fear is something that will keep you in track. Do attend performances by other artist. You will learn different problems people face on stage and other things you should avoid doing up on stage.
At last be good to others and your fans. Never ever consider yourself above them.