I highly recommend stringing with 16 gauge Natural Gut in the main and a 17 Gauge Polyester in the cross.
I string this setup for my 14 year old grandson who plays tournaments.
And I also string this for numerous top 10-14 year old year old tournament players at the club where I string.
Hitting with a quality gut allows you to string it up at a relatively high tension as natural gut hits real well at higher tensions.
If you are not a string breaker natural gut will hit a very long time and is typically very playable until it breaks, so for some players gut can be very economical as well, where many synthetic strings will loose their characteristics after so many hours, that you will want to cut it out, where natural gut will keep hitting well even after many hours.
Where I am, a gut main /poly cross hybrid sting job costs $49 and a full poly string job with a quality string (Luxilon/RPM) costs $39.
You can play maybe 2-3 weeks before gut mains break, but only about 1 week before poly mains becomes unplayable and dead.
So on a per month basis, you can play $39 x 4 or $49 x 2.
In that scenario, I choose the gut mains and not just for the $$ savings, but also for the way it plays.
This is because natural gut doesn't lose the snap-back elasticity in the way polyester does. After a while, poly loses elasticity and stops snapping back quickly. Eventually when they move out of place, they just stay there like a nylon string.
But natural gut always retains its elasticity. And since you only need that elasticity in the mains, put a poly in the cross so it has something nice and smooth to slide across, maximizing spin.
The fact is, if you're stringing your frames with full poly at 50 lbs and higher, and you're a 12-14 year old tennis player, very doubtful that you're bending the strings when you hit.
