Go to your key items, then select your bike, then set to register, that way every time you press select you'll be on the bike and then you can just ride.
This works on all Pokemon games use cheats i suggest action replay from codejunkies or somin or u can use icheat less effective but it still does the job.
Unless you pick it at the start of the game or trade it from someone else, starter Pokémon can't be found legitimately in Ruby. However, there are plenty of hacks and cheating devices that let you...