Website not ending with .com

No... pages rank, not "TLDs"... It doesn't matter what domain has the page. a TLD stands for "Top Level Domain", but has nothing to do with ranking "on the Top"... This simply means it is the highest in the hierarchy of domain structure: Basically, it is comprised of '.com, .net, .org, .co.uk (a ccTLD), .info' and the list goes on (really: this is a short list, these are not ALL the TLD's). There are TONS of TLD's, none of which have any specific advantage over the other (except in some instances of country codes helping with country-specific queries, in some cases). There are TOO many variables in the actual equation of where a page shows up for any given search term(s) for it to be this black and white. The reason that people get confused and think a 'dotCom is the best TLD' is simply a numbers game.

QFE : Thank you Michael; .info is a great example of a TLD that is NOT a .COM; those sites get hella traffic too, I bet. And ALSO: they rank that well NOT because they are a .INFO, but because they are relevant sites with specific, helpful content about their subject matter, and (likely) TONS of back-links to help their rank (prchecker.info has a free website widget that includes a back-link to prchecker.info. Coincidence??? I think NOT!).

and again, Thank you Rashoman; seriously; if you lose one of those "free" sites, regardless of the reason, you do not have a leg to stand on. If it's one of your money site, not only do you lose the income going forward, BUT, you also lose ALL of the work that you've put into ranking to begin with.
I use these free sites as part of my link network only. Good, quality info, relevant context back-links to mine and my client's sites (this tends to work rather well).

All that said; I'd still recommend getting started with a .COM, due to familiarity alone (no other reason). This is your money site, make it good, attract visitors and prosper.

This is true for the most part, but if the .info domain is three times as old as the .com, the .info would probably outrank it. Your mentor is correct though; .com's normally always outrank other TLDs.

That is really not provable.
Regardless of how long your mentor has been doing SEO, he doesn't know (with 100% certainty, I mean, KNOW; how google works). It's just not fair for anybody to say that they "know" something for a fact, when they don't.
You just can't set up an experiment to test the many (unknown) variables that google uses to rank a page, in a way that will be fair to test .com/.info. You can setup similar sites, sure, but make them the same and 1 or the other will be assigned some sort of duplicate content filter (which does exist). Whether that will be the com/info or w/e is subject to speculation.
So, if you make each site 100% unique to test the probability that the filter is impacting the results, then you've muddied up your test by introducing on-page SEO (also, largely speculative) as being a problematic variable. Maybe 1 site happens to have better content than the other, in the eyes of G?
Who knows.
Testing back-links, .info vs. .com ... again, lots of factors which you cannot fairly duplicate precisely in an experimental manner between those 2 extensions...
I have ranked .orgs, .coms, .info, .net/etc, all for different things at different times, and have never had an 'easier' time ranking a .com than any of the others. One of my biggest ranking wins was a .org, while one of my decent money sites (amazon) was a .info.
So, my friend, I do not disparage your mentor; nor do I present anything I say here as fact, either. That would not be fair, as I do not work at google either. This is based on my own process and experimentation, and some basic logic about what factors "could" affect results that are truly outside of our own personal knowledge. I only bring it up because a lot of people miss out on other factors by getting hyperfocused on 'dotcomdotcomdotcomdotcom'. I would pick an exact-match .info over a hyphenated dotcom anyday.

mark, with all due respect to your mentor, that is wrong. there is alot of misconception in the IM world, article marketing/duplicate content being one of the big ones but this one is just as bad. The fact is Google DOES NOT give preference to a website regardless of it's TLD. It's whats in the website that matters, i.e. the content, the backlinking, the social influence and most importantly user experience.

The answer to your question about whether a .com would rank over a .info if both had the same content is i dont know as i've never tried it, but bearing in mind that that would mean both sites having the same content then the google duplicate content filter(NOT PENALTY) would come into play and google will only show the most relevant site, whether that be .info or .com.

but going back to the tld. if you have a look at prchecker.info, as you will see it is a PR7 and sits at number one position for the term PR CHECKER, you will also notice below it is a .net, .org then a .COM, so if google REALLY gave preference simply cos of it's tld don't you think the .COM would be above the .info?

also you may have heard that EDU's/.GOVs being the holy grail of TLDs right?, so you would think that a .gov would rank over a .info right? well type in spain......granted a .com is ranking over the .info for this keyword, but look where the .gov is ranking, and not just any .gov but 2 main US .gov sites, STATE.GOV and CIA.GOV

I am saying this from real experience, people mostly use .COM's cos they are the most common, and thats it, nothing else. Fact is most my sites are EMD .info's and it ranks over most the .com's in the niche's i target.

anyway, as ive said, there is alot of misconceptions in the IM industry, partly due to all the hype created by people pushing their products and partly due to noobs being mis-informed and then passing that info around. If in doubt, get it straight from the horse's mouth, visit the the google support forums and you will find your answer there.