If "age" is your only concern, I wouldn't let that stand in your way. The X is only about two months old (came out early Sept??). Even though phones these days seem to be on the shelves only for about 1yr before the replacement starts shipping, only being two months in isn't that bad. Its out long enough that the initial bugs have been shaken out, but not long enough so that you'd have a LONG WAIT until its replacement gets to market. The G2 came out for Verizon and ATT around Mid September, so its not much newer.
Moto has already announced KitKat is coming. I haven't really paid attention to the G2, so what has LG said officially about either 4.3 or 4.4 updates?
As you say the LG is bigger over all, but does have a bigger screen. Being bigger makes it more difficult to use via one hand only. To me the X is the perfect size. Its marginally taller and wider than my iPhone 5 and 5S, but still packs a 4.7 inch screen. It fits my hand well, and single handed use is a breeze without having to shift the phone around in my hand. It fits in my pants pocket without adding bulk or fear of sitting down with it in there. I thought my GS4 was too big in my pants pocket, and 100% single handed use was not possible due to its size, I had to shift the phone around a lot, yet the G2 is even bigger.
Despite concerns over specs posted by some on the internet, the X feels and reacts faster than my GS4. The screen also looks as sharp as my Galaxy S4, and the X has better reception (based on actual RSSI/RSSP values, not bars!) than my GS4.
The LG G2 maybe a beast when it comes to specs on paper, it may have come out more recently, however its size and UI are a deal breaker for me. But this is your decision, not mine. I've found the right phone for me, Last week I purchased the Developer Edition Moto X for Verizon.