acidic hands...

I had the same problem when I was younger.

The best thing to do is to keep a soft cotton cloth in every guitar case and give the strings, bridge etc. a THOROUGH wipe down before putting the guitar away.  Not just a couple of flicks - I'd say spend at least a full minute wiping down the strings starting with the flat of the cloth on all strings from the bridge all the way up to the nut, then pinch each string individually between the cloth and two fingers and run up & down each one.

Then spend time wiping down the bridge, saddle and upper bout and basically everywhere that skin might have contacted the guitar.  Don't forget the pickup covers too, which might have got some sweat on them.

Ever since I started being fastidious about this cleaning regime, my strings have lasted a LOT longer.  As Ron suggested above, you can use things like Finger-Ease etc. to polish the strings and that will make them last, but some people don't like either the smell or the feel of such products - try it and see what your son thinks.

You are not being specific.  Do you mean there is a ton of crud in the larger wound strings, and or a screech in the thinner gauge strings? And it seems to be wearing out the strings faster? 

The Finger Ease and Fast Fret ideas and other cleaning regiments are fine and highly recommended, especially for someone tending to spend countless times on the darn instrument. 

Which takes it to the next step.  Good hand and finger grooming are imperative. The results hinge greatly on the relationship of (poor vs. good) fingers hygiene to string life.  Always clean, well manicured nails of desired length with proper cuticle care, and most definitely fingertip skin maintenance...building up callouses is great for learning or playing something so "out there" unprotected fingertips cannot bear up the friction, even WITH the lube, but the callouses will bring the pollution in and string changes might include emery board and / or pumice stone (grades vary like sand papers, etc.) removal and smoothing for the fingers.  The trouble with the finger lubes is overuse, abuse, and over dependency.  Wasting a can a week of it won't make anyone a better player than one that lasts a month or longer in general.  Nominal amounts are usually suffice-yes, depending on playing style and preference of that all important "feel".  But fastidious was a word used, and look it up if you don't know the meaning, fastidious attention to detail is paramount.  Don't be afraid to put some women's  facial grade product (not the kinds that exfoliates or are themselves acidic!!!) like Oil of Olay into hands (usually a while before playing, and not being shy to wash and thoroughly dry hands just prior to actual playing), nor shy from meticulous wipe down of strings (being EXTREMELY careful not to get significant quantities of ANY product into fingerboards!!!!! Wood friendly products can be used, again SO much Discretion is needed-too much cannot be backed out of, whereas not enough can gradually be stepped up to best determined level.  I do use Liquid Gold.  I will remain silent on wood soaps-do not mess up is the alpha and omega of fingerboard care!!!  Frets and strings can be cleaned with metal polishes and even isopropyl alcohol (good for first stage of large crud cakes or buildup removal) most carefully of course, using artists horsehair brush (or similar synthetic, varying type and stiffness, widths / lengths, bristle counts, etc. available) and dried by cloths, mouth blowing on, or blow driers.  It is all in the details.  Just treat your stuff good.

You can get a bit complacent if you have scored oodles of strings, but a good habit makes "new" a constant quality of showroom AND professional playing ready guitars of any kind.

...But then maybe you need to catch your favorite strings on sale and buy in huge bulk regardless!!!

String of Hits Rocking ON & Keep the Cleanly Faith,
Rocket

...dry baking soda dusting of hands can help some cases too! ...Clint Eastwood voice: " A  man's (or woman's) gotta know his (or her) limitations."

"He still doesn't charge for mistakes! "
http://jbonamassa.com/tour-dates/
"Everybody wants ta get inta the act!"
“Now, this isn’t your ordinary party crowd, here.  I mean, there are professionals in here.”

Hemp conditioners are fantastic if you can find them.

Rock ON & Keep the Faith,
Rocket

"He still doesn't charge for mistakes! "
http://jbonamassa.com/tour-dates/
"Everybody wants ta get inta the act!"
“Now, this isn’t your ordinary party crowd, here.  I mean, there are professionals in here.”

Exlier Nanowebs (not polywebs).  Great strings - my fingers eat through strings in a week, and they noticeably degrade after just a couple days.  With Nanowebs I can get a couple months out of them.  Worth a shot, I've been using them for 10+ years and love 'em.  Personally, I don't like Fast Fret at all.  It feels weird, and didn't prolong the life of my strings; but different strokes for different folks, I know a lot of people do like it.

I agree with everything else said above - keep your hands clean and wipe down the strings after playing.