Without reviews or board posts you can search I don't know of any way to tell.

If a member writes reviews, you can see when his earliest review was submitted. If someone posts on the boards, you might be able to find his earliest post through searching. If he is a frequent poster enough to be n the top ten posters list of a board, then it will say 'member since...' but anyone can elcect to not be in the top ten posters list by turning it off in their account manager.
So, while you can sort of figure out how long some members have been around, for the most part the answer is no.  

Besides just 'being' a TER member (with no reviews, board posts or whitelists) should not be good enough screening info for you. Anyone can be a member. YOu need to come up with other screening methods (job info etc.) If someoen cant provide you what you need as far as references you can either come up with other creative screening methods, or just do not see him if you are not comfortable. Your comfort and safety is the most important thing.

Here is something I did way before I had good provider references and before I was a p411 member or whitlelisted on TER: I am also self employed, so was not able to be verified through work info, but I once gave a provider ( a reputable and well reviewed lady I figured I could trust--I would not do this for just any provider) names and contacts for three of my clients and described the kind of work I did, and asked her to contact them pretending to be in need of my services. Of course that would not tell her if I was a good client for a P4P session, but it would tell her something of my character and reputation, and that I was who I said I was. Obviously this would not work for everyone, but just to show there are other creative screening methods that can be used. The main thing is that both parties have to be comfortable with the screening or the date should not proceed.

It's my understanding that TER won't accept reviews where the encounter took place more than 3 months prior to the review.

...in ascending numerical order.  Today, new members are issued numbers over 2,000,000.  My number is around 61,000 and I've been a member since 2002.

2,000,000!!  That's a lot of horndogs!

will see I have been a member here since Sept. 2002.