Tails has always stuck with his big bro Sonic through thick and thin since the genesis days. Weather he's piloting a robot mech or just playing an supporting role, he's appeared in nearly every sonic game, including starring in his own games on the game gear.
Is Tails really 8 years old, I tend to question SEGA for their stupid character age crap (like how Charmy went from a 15 year old to a scatterbrained 8/6 year old and Amy in CD being 8 and SOMEHOW surpasses Tails and Charmy's age and becomes 14). I think Tails is 12.
How he get two tails, who knows. In Japan, fans call him a Kitsune, which is a demonic fox spirit said to have 9 cursed Tails. When Tails get's older, he may grow more Tails, perhaps becoming evil and extremly powerful and take over the planet.
I loved Tails in Chronicles, He indeed matured alot in that game and his moves were very useful.
Chronicles notes how very similar Tails and Eggman are, almost as if they developed a father & son relationshp. I think he might have been heartbroken at the end of chronicles (play the game to see why).
I just want to say that I believe that Tails has control over Electricity. This comes from Sonic Heroes and Riders. His Thunder Shoot and Electric Plug attack. Plus: Plugs dont create electricity. They get electricity from something.