Most teenagers celebrate turning 18 by heading to the pub to buy their first legal pint, but not Jonny Innes.
Instead he'll be putting on his trainers and running 26.2 miles along London's streets.
That's because on Sunday he turns 18, becoming the youngest person to take part in the London Marathon this year.
The keen runner, Jonny, from Truro in Cornwall, has been training four times a week and says he's "really excited".
And Jonny told Newsbeat he'll be putting on Taylor Swift's Shake It Off to help him along the way.
But the teenager won't be jogging along to the pub after the marathon.
"I may leave it a few days after the end of the race to let my body readjust back to normal."
Plus there's the slight issue of school the next day.
So what do his mates think abut his choice to run a marathon instead of partying with them?
"They don't really know why I'm doing it. They think I'm a bit crazy."
Jonny is running the marathon for the National Society for the Prevention of Cruelty to Children and has raised several hundreds of pounds so far.
"I chose to run for NSPCC because I've had quite a fortunate childhood and I know not everyone has been as lucky as me so I'd like to give something back."
The teenager will be one of 36,000 runners taking part in Sunday's race and he hopes to run the 26.2 miles in 3 hours and 45 minutes.
"I'm really excited. Having watched it four times before the atmosphere is just crazy."