First off we need to remember that at your age you can't legally own an RIF (or any airsoft gun for that matter). I'm supposing this is going to be your first, so I'd caution that it's going to probably cost you in the region of £500+ if you include the gun, kit, tank, regulator and line.
That all said, I've had a lot of fun with my M249 so far, but there are so many options out there for airsoft guns that turning down two decent RIFs in favour of one HPA setup seems a bit silly to me if it's your first. I certainly don't feel like I never want to go back to my GBBRs either - my feeling is HPA is just different, but not necessarily better. Airsoft has never been entirely about having the best and most consistent gun to me, and I think the problem for some HPA users is that they get tagged as 'play-to-win'-ers. A slim minority deserve that title.
To address the bit about FPS: Yes, there's a stigma that comes with HPA setups. There are tournament locks out there that mean you can't change the FPS easily during a game and should people's minds at ease. I know the Redline Firebase has one built in, but they only cost a few quid for other regulators.