Welcome to the forum Louis.
Mouthy players can be a challenge, especially given the relatively small age gap between you and the players. Out of interest do you card at this age group and if so, have you carded any of this players team mates?
Ref'd a particularly challenging player on regular occasions that played for my son's old team, no respect for authority, wants to argue every decision, constantly arguing with team mates, my dads the coach so I can do what I want etc. One particular game he was at his annoying worst due to being on the wrong end of a heavy score line and the usual world is against me chip on the shoulder attitude. After committing a fairly petty foul, I called him over, he ignored me and started to walk further away. I stood my ground, loud blast of my fox 40 and sternly called him back (loud enough that everyone in the area of the pitch could hear). He came back with his tail between his legs looking rather embarrassed! In the games I have ref'd since that he's played in, he's never tried it on with me again, possibly in part because of the public dressing down he got on the touchline from his coach (dad)/ & mum after the game in front of his team mates and the groveling apology they forced him to make. If anything, whenever he sees me refereeing one of his games now, he almost looks scared!
The comments that you mention should definitely be dealt with as it's dissent. The player is openly questioning your ability and authority as the referee. If players see him get away with it, they might try it on as well. Any player regardless of age who tells me to "do your job" or "blow the whistle" etc gets a talking to at the very least, usually along the lines of "I don't tell you how to kick the ball, don't tell me how to ref". The older they are, the sterner it is and depending on what and how it was said would probably be getting a card as well.
As others have suggested, try mixing your games up a bit to broaden your experience. By all means, continue refereeing for this team if you feel confident enough in dealing with this challenging player. If he or any other player speaks to you in this way, deal with it the first time, don't allow them to get away with it for most of the game then try to take action. Stamp it out early, either by the stepped approach (firm talking to, calling the captain, card etc) or if you feel the comment is serious enough, then card him straight away, making it clear to him and all the other players on the pitch that this kind of behaviour and disrespect will not be tolerated!
Good luck!