The legal position:
You're 14. It's an offence for you to buy any imitation firearm, realistic or otherwise, or for anyone to sell one to you. The only way you can get one without an offence being committed is to be gifted it. At the point of transfer to you, it doesn't matter if it's realistic or not (because of your age), only that nothing changes hands from you to the person gifting it.
The practical position:
Once a realistic imitation firearm has been sold by a retailer, the State won't take any interest in where it's transferred later, as long as it's used sensibly. If it never gets taken outside to show off to your mates, no problem. If it's taken in a bag, in a private vehicle, to and from an airsoft site, nobody will ever care, and nobody at the site will ask how you got it.
The dad position:
Talk to your parents about owning and using an airsoft gun, and getting to and from sites. Whether you can get a gun, and whether you should get one, is really down to them. I'd repeat the advice to go and play airsoft as a rental at least once before thinking about buying anything. It's a great hobby, but it's not cheap, and YouTube videos can give a false impression of the reality. The classifieds are full of guns that were bought on a whim and then never actually used to play. Don't be that person.