I got into the .223 Rem late in life, after many years with the .22-250 Rem, which served me well, but I had the chance to pick up a used Tikka 595 for $300 and bit on it. It was one of the best gun buying decisions I ever made.
The .223 Rem cartridge has never failed to impress me with it's lack of noise, recoil, and barrel heating. It will shoot 10 shot strings at the range, hardly heating the barrel at all. It's extremely accurate and tolerates many different gunpowders, bullets, and loads with high consistency.
Although I'd shoot a deer with it, using Nosler Partitions, I'd hesitate recommending it for a youngster without considerable shooting experience. The youngster could gain that experience by successfully shooting the .223 for several outings, then go on a carefully supervised hunt, hopefully for smaller game than deer. If that hunt is successful, deer could be next.
I've been on hunts where someone has wounded a deer and ended up tracking and sometimes finding it and dispatching it. It's probably not the thing to have happen on a kid's first deer hunting experience.
People are like rifles. Some are tried and true, having great eyes, personality, and fun to be with. Others never seem to hit the mark with you. Still others go off half-cocked. Still, it's nice to know most of them.