Not only is this a great question from a workout point of view but I also work for a breast center so I can get a bit into this one.

Breast tissue is primary composed of two things: fat and glandular tissue. As we get older, unfortunately, the breast begins a downward cycle of moving from glandular to a more fatty makeup. In fact, did you know that your breast do not even mature until after your first child? This means that post birth the cycle is starting. Which is good for you.

To get the breasts you had in your early twenties is going to be challenging. There is nothing that will change your breast in a reverse cycle but there are quite a few tricks you can do to get them to appear as if they are.

1. Since the breast is fat if you lose weight then you are going to lose breast weight as well. For some women (including myself) this is the first place I notice weight change. Now the bad part is you can not target weight loss areas, so if you do not want to lose body weight in other places as well then you may be out of luck. But with a healthy diet, increased cardio, and more weight training the weight will come off. My thing is if the girls get smaller then there is less to be "saggy".

2. Train the pectoralis muscles. These are the muscles that find a safe haven behind the breasts. When you look at a guy with nice pecks, try to think how that might help your chest look if they were behind your breasts. You have two pectoralis groups: the minor and major. Both need to be worked to get the greatest benefits. How do you do that? Use heavy weights to help gain mass. 3 set minimum of 3 reps is best. So think 95% or more of you 1 rep max.

Here are some recommended exercise moves:

Incline chest press

Standard barbell chest press

Rows

Pullup

Punching a punching bag

and the ALMIGHTLY PUSHUP

are all great workouts. For pushups and pullups just do as many as you can till failure.

Think, if you are losing breast fat but gaining chest muscle your breast will still be very much there, just perhaps may remind you of your youth!

TIP: If you ever think of getting implants please consider only having them placed in the position surgeons call "behind the muscle" . The implant is placed behind the peck muscle. This is better because when the time comes for mammograms, which should first be done between ages 35-40 then every year after 40, it allows the breast tissue to still be observed and if for some reason additional procedures need to be done (biopsies, ultrasound, treament) your radiologist will thank you. That is my soap box speech.