Maria was much more active this year than Serena was at 17, so of course Maria has better results. Also, since Maria has a 2-1 head-to-head edge, one could say that Maria is better at 17 than Serena is at 23. I wouldn't, but someone could.
"He who finds a wife finds a good thing, and obtains favor from the Lord." -- Proverbs 18:22
"Hard work beats talent when talent doesn't work hard." -- Herb Brooks
"A man who views the world the same at 50 as he did at 20 has wasted 30 years of his life." -- Muhammad Ali