I love a boy who is older than me.and he doesn't know me. What will I do

First, that's not love. You have a crush on him. Love is only possible when you know someone for a while, it is something that develops with time.

You smile and say hello a few times in passing, without stopping. Then you say hello how are you, with a little pause so he can answer just one word or stop to talk a bit. Or hello isn't it a nice day, or something else small and not personal.
After 10 or so times, you will know if he wants to know you better.