I posted this on another board in response to the same question:
On keeper specialization, which is a perennially controversial subject, here are a few thoughts I have based on 14 years coaching rec and rec plus (tournament and all star) soccer teams and 8 years being involved with and managing mid and high-level club teams (with professional coaches), plus having one son who started playing GK early, one who played a little early only because he was willing and he was the coach's son and then played again for part of a season of HS when he was a little dinged up and they were desperate, and two others who wanted nothing to do with the position. I've coached or managed teams from U5 to U19. Consider the following three scenarios at ages 9-13 (since few play GK exclusively at 6-8 and many play GK exclusively at 14-18):
1. A kid who wants nothing to do with playing GK: If your kid doesn't want to play GK at all, then they shouldn't play it except if the team is rotating everyone through goal. Even if they are good at it, by all means don't let them get pigeon-holed in the position. That's true even if they are better at GK than on the field and they will be sitting on the bench otherwise. Find a team more appropriate to their level if possible rather than force them to play GK when they don't want to do it. Make sure they know not to ever volunteer that they can play GK when they are trying out for a new team. Playing GK on a regular or semi-regular basis when the kid doesn't want to do it will spoil the sport for them. I take it no one disagrees with this, although there are some who don't think you should even put a kid in the rotation in an "everyone takes a turn" system if it's going to be traumatic for them and I have definitely made concessions in some situations.
2. A kid who likes playing GK, but also wants to play on the field: This is the tough case. Frankly, the kids who do this often end up being weaker at both positions and I have seen several leave the sport early even though they showed great promise early on (in part because the reason they were good at both is because they were a bit more athletic than the other kids on the team). Both positions require great technical skills and they usually underdevelop both of them. It doesn't have to be this way though. There is absolutely no reason that playing a half in GK should stunt a kid's growth on the field as long as they play the other half of the game on the field, they attend two practices a week and play on the field 75% of the time at practice, they do skills training on their own or at the club's optional Friday skills clinics, they attend a summer soccer camp as a field player, and they go at least every other week to the club's separate GK training practice with a GK coach or they do private training in lieu of the club skills training and/or the club GK training. The reality is that most of the kids who do the split GK/Field play aren't committed to either (they often just want to be in the team with their friends or to be on a top team), which means their parents aren't committed to either and the result is that they don't do much more than go to their team practices and maybe occasionally a GK session. That's not the end of the world (soccer isn't everything), but it's not surprising they fall behind their peers.
3. A kid who wants to play GK full-time. This is what people often mean when they ask about specializing, but those who flatly reject it are usually thinking about the first or second scenarios. I'm talking about a kid who wants you to shoot on him all the time, who begs to play GK in the game before there are full-time GK's or who always wants to get to practice early and asks other kids to shoot on him. These are kids who tryout as GK's and, although they might say they are willing to play on the field if needed, their first choice is GK. Do you let them be a full-time GK at 9 or 10? Arguments that this will harm the development of foot skills and field awareness, while worth consideration, are not inevitable. If they play 75% of the time in practices on the field (e.g., warmups, drills, 5 v 2's etc), go to their club's skills training, work on juggling etc on their own, and watch a lot of soccer without being prompted, they do just fine. If they play on the yard at school and/or for their school team, even better. Add on to that the club's GK training sessions once a week and a private GK trainer and/or agility trainer once a week and both a field player soccer camp and a GK specialized soccer camp over the summer, and they will be great. Of course, that means that your kid and their parents are REALLY into being a GK and into soccer generally and they want to play all the time. Overuse is not really an issue (or anymore an issue than for field players) because the muscles and skills used for GK are so different than that used for a field player most of the time that it's like playing two different sports. Sure there is a possibility that they will physically underdevelop and not be able to continue as a GK after puberty, but if they've been doing the other stuff with the ball work etc, they can be fine. Is there a possibility they can't stay on the team because they aren't as skilled five years later and they haven't grown into being a keeper with a full-size goal? Yes, but most (and I mean more than 50%) of kids in every position quit before high school and if a kid wants to play GK now, why deny him pleasure now because he might want to keep playing five years from now and might want to stay on this team?
So, the real question I ask parents and kids (and I asked myself when one of my kids really wanted to play GK at an early age) is how passionate is he about doing it and how committed are the parents to supporting that passion. In other words, if the kid isn't going to do skill work on his own or with the club, doesn't really watch the game on TV, and just wants to play GK because he likes to get dirty and he doesn't like to run very much, then try to delay starting for awhile until he is a little bit more mature to understand what the position really entails. If the kid, however, understands that he needs to work on both parts of the game and, as a GK, he will have to essentially do twice the training of other players, and he looks excited at that prospect, then he's ready.
