Around the middle of the second summer the average keeper should be able to tell the gender. Some breeders can very accurately sex them at a couple of weeks old but I have no clue how they tell.
The best way for us regular folk to sex them is to feel on either side of their cloaca (butt). Males will have what feels like a bb on either side. Females will not. I'll give you two guesses as to what these little balls are...
I suspected my male to be a female based on random speculation and guestimate comparisons. When he woke up from hibernation after his first winter I could not feel the little bb's. By mid summer I could. Around the same time he just started to develop fat jowls. At the end of summer his jowls were noticeable but not huge. Now, half way through his third summer, his big fat male Tegu jowls are unmistakable.
Their first summer they are tiny and adorable. Mine was around 16" when he went into hibernation...
Holy smokes! I couldn't believe how fast he grew his second summer. He went from 18" (May) to 40" (October) that summer putting on literally 1.5" per week for several weeks in a row.
This summer he hasn't been growing much in length (currently 46") but wow is he putting on weight. I haven't kept an accurate weight reading as he grows but he a bit over 9 lbs (4 kg or 4,000 g).
The best part though, he's sweet as honey. He hasn't once bitten anyone. My 6 year old niece can walk right up, scoop him up and play with him (her little friends think she's so tough when she does). He gets a bit of an attitude when it's time to come back in after free roaming in the yard, but besides that he's nothing but a big ole sweety.
I am firmly convinced that the keys are frequent (daily) human interaction coupled with a proper environment. I am thoroughly convinced that when kept in tight quarters the animal is constantly stressed which results in being constantly edgy. Aren't you a bit irritable when you are stressed? I know I am.
It's tough to supply them with a big enough enclosure, but if you can, I would recommend Tegus to anyone interested in reptiles. Mine is in an 8' x 3' @ 3.5' tall enclosure and spends several hours most days on a 10' x 6' outdoor balcony. He's spoiled rotten
PS - Written by Toby...