A balance
Seb320, I was in your position a few years ago so thought I'd give you my two cents seeing as usual on PPRUNE is under-represented by actual glider pilots. I started gliding at 14, went solo at 15, and got my first flying job as an instructor at 18!
Unless you've got big pockets right now, Gliding will get you futher and more experience than power flying will. With some flying schools charging upwards of £150 an hour just for a battered Cessna, it's very difficult to make much progress at all, one maybe two if your lucky lessons a month? Throw in learning to drive, getting a car, girlfriend etc and finances can be a bit tight to learn to fly power that easily, unless you get a PPL scholarship from HCAP or the Air League etc which in that event, go for it!
Gliding is by no means inferior if you choose it, British Airways take their work experience candidates gliding, the most recent deputy recruitment manager in BA has a big gliding background, CTC Aviation partnered up with clubs, the air league and the BGA a couple of years ago to offer 16-18 year olds the chance to glide. So there's definitely some recognised merit and I've found it far easier applying for aviation jobs with it.
Don't listen to all those that say gliding is just about standing around because that culture is fading, during the winter flights are obviously shorter due to the weather, but gliders generally fly in more conditions than your regular spamcan anyway. And where else during the summer can you fly for a couple of hours for less than the price of a circuit? Oh and as for being "disorganised", my club do over 25,000 flights a year, and never have an issue with serviceability of aircraft unlike small flying schools.
As for the skills and opportunities, as many have said stick and rudder skills are good and will at least give you a sense of coordination which will test your aptitude, you'll learn to read the weather, meet people from all different backgrounds from lawyers to factory workers, senior, current and ex airline pilots all with connections (Which if you haven't worked out yet are vital!). You'll almost certainly have more fun flying gliders too, it's not just flying in straight lines for bacon butties, there's always a challenge and many people move onto aerobatic training which is out of this world, two 17 year olds from my club are on the British Aerobatic Team going to the World Glider Aerobatic Championships, both went solo at 14! So you're by no means the youngest!
If you get competent and get to licence standard in Gliding you can then convert to powered for less hours, some clubs have a motorglider that you can learn to fly for £80 an hour, from there it's a conversion at a flying school onto SEP. Then if you're still keen there's the potential to hour build flying the towplane, my friend who's just turned 19 now has 300 hours half of which on tailwheel towing gliders, you can't possibly turn an opportunity like that down, it could save you thousands if you ended up going the modular route.
Or when more experienced in gliders, you could mix it up, and you could teach people to glide in the UK and abroad as a gap year, my friend did that at London Gliding Club whilst flying the towplane on and off, he then finished his CPL and now flies 737 for Titan at 20 year old! More often than not you'll get your instructor rating paid for and a job offer too, not many avenues in flying are as accessible as gliding!
Cost of gliding? Your local club at Ringmer near Lewes charges less than a fiver for a circuit and only £11 an hour for glider hire and no instructor fees. Absolute bargain for under 26s, probably one of the cheapest places in the UK! That area is beautiful and in northerly winds is fantastic for flying at high speed along the south downs! Parham Gliding Club is not too far away either!
Plenty of scholarships too, if you can get yourself a PPL one then go for it, but there's lots of gliding ones available too to get you solo for free, up to licence standard and beyond.
Check out UK Junior Gliding too online, see why thousands of other young people have learned to glide and made gliding the best junior movement in GA?
Gliding certainly requires more time than power flying, but as usual, the more you put into flying, the more you get out. You'll generally be asked to commit at least half a day, but you'll get a lot of skills from maintenance to airfield operations and maybe even driving the mower! All good things from the CV!
But ultimately, It's your choice, fly once or twice a month trying to scrap together a PPL (£10,000+) unless you're loaded and then wonder how to fund an ATPL or go gliding for next to nothing, have an easier and more diverse route into power flying and maybe save yourself some cash when it comes to hour building?
Oh and if you are considering doing an integrated ATPL there's no point doing a PPL as you'll be made to re-do it all again, or worse, be rejected for having too many hours (there is such a thing as too much experience!)
I hope that gives a more balanced view, I had exactly the same dilemma but I would be broke if I had tried to do a PPL at 16, feel free to PM.