I can look pretty old in photos, but also have the advantage of doing photography as a serious hobby (have all the gear) and have got pretty good at taking flattering photos of people!
It's all to do with lighting - if light falls at the wrong angle onto your face then lines and shadows will be accentuated, so you need to make sure that light falls evenly onto your face, with as little shading as possible.
If you're going to take a selfie with your phone, go and stand by a window and make sure the light is falling onto your face (you may have to experiment a bit with the angle/direction of your face), but it will make a big difference.
If you're having your photo taken outdoors, the shadow effect will be a lot worse if the sun is shining as you'll get loads of shadows on your face (for this reason, wedding photography is a nightmare if the sun is shining). Either use the flash on your camera to fill in the shadows, or move into the shade.
I've got a big circular reflector which I use to bounce light onto the face - it gives a lovely radiant effect (I've done quiet a few portraits of friends so that they have nice, natural pics for dating sites etc) and will shift unsightly lines. You can get a similar effect using tin foil stuck to a piece of card!
Finally, when I'm trying to get people to pose naturally for photos, I get them to turn away from the camera and relax their face, then turn towards the camera and smile only at the very last minute, so that their expression is more relaxed and natural.
If I had the time (v difficult with a small baby) I would spend all my time taking nice photos of people to cheer them up!