1) Yes. Apparently the tests are "easier" for younger people (quicker reactions/can adapt more quickly and other such psycho-babble reasons)
2) The vast majority of commercial pilots pay for their own CPL/IR. Sponsored cadets make up a relatively small group of the pilot community. Only you can answer the question whether it is worth it or not.
3) Sponsorships are few and far between, and the majority in future are likely to be of the CTC variety where the candidate will have to sign up for a bank bond of around £70,000 followed by 5-7 years of reduced salary and tied to the "sponsoring" airline. Starting as early as possible is probably a very good thing.
Do consider further education though. Aviation is a very cyclical industry and the potential to lose your livelihood quite real (loss of medical, fail sim check, airline going bust etc etc) and having another string to your bow is always useful. The experience of a 3 or 4 year college or university course will make you a more rounded and mature individual.
Have a read through the
Archive Reference Thread for more information.