I didnt think you could own one if you were below 18?
However you could try asking
@SeniorSpaz87 I think he imported/exported some
I have imported many RIFs into the UK. While they are completely legal here in the states (for the most part) there are a few things to consider.
1: Where in the US are you planning to fly? This includes connecting airports. Some states like California have rules that make UKARA shudder.
2: Do you have orange tips?
3: Getting them back in.
So first off, I have imported probably somewhere in the neighborhood of 30 RIFs into the US, 90% of them in my own suitcase. These ranged from single GBB pistols to an entire suitcase with a MP40, L86, MP7, 3 pistols, and mags for everything (yea, Heathrow security confronted me but once I proved they were airsoft and I had UKARA they let me through no problem). What I always did was to paint my tips orange. Go out and get some cheap orange spray-paint (you'll have to get an adult to buy it as I believe you have to be 18 to purchase spray-paint in the UK), paint up your tips, and you're good to go on that front (unless going into a "problem" state like Maryland or California). Furthermore, batteries. You can not put LiPos in your checked baggage. I have never brought airsoft batteries over to the US, but I've brought drone and RC batteries both ways several times. I brought them over in my carry-on and had no problems, although personally I think security might not like airsoft batteries (they tend to look kinda "exposed", unlike the enclosed LiPos I've brought over before, so take at your own risk). I always put them deep enough into my luggage (usually wrapped in a shirt or two) that they don't leave an outline, but close enough to the top that security doesn't have to dig for them, and right at the zipper of my bag I leave a nice long note stating they are airsoft, have orange tips, and a copy of legislation stating they are OK and do not need to be in their own bag (lots of airsofters over here think they need to be in their own locked bag, which they do not. Feel free to do this for added safety, but it is not required). Finally, I would put a TSA lock so some random bag-man couldn't steal them. I would also check with my airline if they were allowed, but since I always flew United I knew they were fine after the first time. Expect your bag to be opened at least once (I had it opened at three airports once, and I've also had times where they never opened it at all). I never had a single gun seized following the above in probably 20 total trips.
Now your main issue is getting back into the UK. I expect Heathrow to have a SERIOUS issue with you bringing them in. Your bag will be pulled. You will have to go to security to get it approved. It will take a fair bit of time. And in the end they may not let you bring them into the country as you are required to have UKARA to IMPORT RIFs into the country, not just buy them, so bye bye to your RIFs if that happens
. However, if you are travelling with your dad and he has UKARA, if he can prove that then you should be fine. I would put his UKARA number on the letter in your bag to attempt to expedite the process. If no one you are travelling with has a UKARA number you might be stuck in that regard.
So, getting them here won't be an issue if you've got common sense, but getting them back may be hard. Where about in the States are you going? I may know people who can help you out on this side, maybe rent or borrow from them. Failing that, if you are not confident in your ability to get them back to the UK you can always rent as mentioned above.