"I am over the moon; I was away in France for the European championships during my 17th birthday but we wanted to get it done quickly so I signed when I got back," he says.
"I love West Ham to bits, that is who I want to play for, and where I was brought up."
Mark has one more tough week to go of a campaign that has seen him mature rapidly, and he adds:
"The gaffer has got me and Chrissie Cohen involved all the time now with the first team and we are in the squad for the final.
"I am pleased about that because it gets you involved and gives you a taste of the atmosphere."
Training with the first team is not new to Mark, though, and he adds:
"The first time was when I was a schoolboy under Glenn Roeder; he got me in from school and I trained for about a week with them.
"It definitely helps, training with the first team, and they do clever things; you pass to someone and don't think you are going to get it back, but somehow they do get it back to you and it is just brilliant - everyone is on the same wavelength."
Mark knows that there is nowhere better to continue his education than Upton Park, and he adds:
"It is the Academy of football, as everyone says; they bring so many good players through and are not afraid to put the youth in, as we have seen from Chris Cohen this year.
"He is a big lump already! He has proved he is good enough to do it so, good luck to him.
"As for me, I will just keep working as hard as I can in the reserves or whatever - that is all I can do, and hopefully I get my chance."
Regarding the playoff final in Cardiff, Mark says:
"I think we will win it after our performance against Ipswich the other day; everyone is on a buzz.
"I wouldn't pick one of Palace's players over one of ours, and I think we will win 3-0 or 4-0!"
Mark was captain of the England U17s that finished fourth in the recent UEFA tournament in France, and he reflects:
"I only played three games - Ukraine and Portugal, which we won 2-0 and 3-1, then I was rested for the third game against Austria as we had already qualified."
His third game was the semi-final with Spain, when Mark was harshly adjudged to have committed a professional foul on Marcos Garcia when the pair got tangled racing for a through ball late in the game, and he was sent off with Spain scoring the resultant penalty to win 2-1.
"It was a bit of a gutter because we should have beaten Spain in the semi-final; it was unlucky, but that is the way it goes in football," he says.
"We played so well against Spain, but what happened was unbelievable, going out to a late penalty.
"I just want to focus on the club now and put all my efforts into that.
"It is a brilliant atmosphere in training and everyone is having a laugh and a joke off the field; on the field it is done seriously, though."
MD Paul Aldridge is delighted about Mark's signing and says:
"This follows on from Chris Cohen signing a professional contract recently and indicates that the future of the club is bright."