Recently I've noticed a pattern of comments being left for new users who leave "late answers" which show up in the "late answers from new users" review queue. The general gist of many of the comments I'm recently encountering is as follows, whether the answer is well-written or not, and whether the answer is excellent or not:
"Why would you want to answer a four-year-old question with an accepted answer?" (Substitute one to seven for four, depending on the question answered late.
Sometimes the comments I've been seeing recently are even nastier, and may go on to include:
"Do you really think your answer is an improvement over the accepted answer? Are you kidding?"
I'm not here to name names, so I'm not citing "real" reviews displaying such sarcasm; but I think some new users wanting to participate by answering questions may first take a stab at answering old questions, just to get their feet wet, before "jumping in" to the "race" to answer new questions. It's safer to do that, or so it should be, I think.
Don't get me wrong; sometimes "later answers from new users" are mere spam, or un-formatted and nearly impossible to decipher, or are not answers, but questions, or consist of opinions and rants, or are just plain wrong. Those posts should be addressed, in comments, or by voting appropriately.
But when a new user interested in answering questions first takes a stab at answering an old question, takes the time to learn and practice using mathjax, and meticulously writes a good, correct, and careful answer to an old question, I think we should be encouraging them, even if just to say: "You did a really nice job answering this question; I'd encourage you to expand by answering newer questions." Or: "this was really well-written!", or "Thanks for the use of mathjax; in the future, you might find it even easier to use ... instead of ...".
Reviewing late answers from new users, when they are sincere attempts to master the art of answering a question, should not be met with sarcasm or disparaging remarks. We are given a great opportunity to pass along encouragement when appropriate, and/or helpful suggestions how to improve an answer.