He's seventeen and a half, so lying is something that is not uncommon in male teenagers who feel (no matter how unreasonably) their newly achieved independence and privacy is being threatened. So first of all it's probably a 'phase' rather than something inherent.
I had to do some reverse engineering to find his approximate natal details, because I use different methods than those expected by astro.com, et al.
His is a day chart which makes Mars, the planet that is likely to cause the most difficulty. Mars is squaring his Ascendant, in a dominant square (in the order of signs). That suggests that he's a prickly sort of character (though there are other factors which might overcome this). Mercury rules not only his Ascendant but also his tenth, where Mars is located but Mercury is not placed well, being just inside the twelfth house (I use whole sign houses) and is averse to the Ascendant. That suggests that (at least initially) he has some difficulties finding his direction in life. Furthermore, Mercury is squared by Saturn in Taurus. This too is a dominating Square. Saturn isn't a major threat in a day chart but it does indicate difficulties and things that can be surmounted through effort. The Saturn/Mercury square makes him defensive and perhaps wanting to exclude the outside world if he sees it as intruding.
The squares from Mars to the Ascendant and Saturn to the Ascendant Ruler, which itself is badly placed, are the key indicators of difficulty in his chart.
Given Mercury's natural rulership of communications and that it can be a 'trickster' I think we have clear indications of lying, from these aspects (this, as Dave points out above is nuanced to your description of the situation, there are other meanings and manifestations that are possible).
There is hope and quite a bit of it. Jupiter is the benefic of sect (most helpful or rewarding planet in his chart). Jupiter is angular in the Seventh and is in it's own sign of Pisces. It rules his Lot of Fortune (in Sagittarius) and whilst it squares Mars, it is in the dominating position. So he can overcome his Mars tendencies but that won't necessarily happen automatically. That being said, he's only just on the verge of adulthood, and he's a lot to learn.
One last general point, Mercury rules his Lot of Spirit which is in Gemini and so co-present with Mars. Fortune indicates the 'slings and arrows' he will face from life (factors outside his control). He looks likely to be quite fortunate in these.
Spirit indicates his ability to assert himself over those factors and take control of his life. That sadly is rather weak. I think he's likely to be someone who does well in life, not so much by his own efforts but by being in the right place at the right time. If he uses some of his positives, he can be quite charming and attractive. The issue is whether he's going to be able to do that.
OK, so much for the generalities. Were you looking for something more specific?