I'm 19 years old and I have saggy breasts. Would exercising help this or is it too late for me?

It is not likely to have saggy breasts at the age of 19 unless you have very heavy breasts. To be honest, exercising doesn’t help too much but if you are exercising, wear a good quality sports bra. For further information, please contact a board certified plastic surgeon that can guide you properly after examining your breasts.

Thank you for
your question.
It is difficult to be experiencing significant breast ptosis
at such a young age, but you are not alone. A large number of women have
similar concerns.
Current research highlights the following as risk factors
for sagging:
Greater age, History of significant weight loss (>50
pounds), Higher BMI, Large bra cup size, Pregnancy, Smoking
As women age, the Cooper’s ligaments – the connective tissue
that helps breasts keep their shape- stretches out. Aging also causes breasts
to transform into having more fat rather than breast tissue making them less
perky and making them appear deflated.
Although you cannot control the natural aging and sagging
effects, or a genetic link, factors such as weight fluctuation and smoking are
in your control.
In fact, maintaining a healthy weight is important because
the higher the ratio of fat to breast tissue within your breast, the increased
risk of breast sagging. Having a healthy diet will also be protective (i.e.,
slow down) of aging effects and sagging effects.
Also, please note that breast sagging worsens with the
number of pregnancies you have, and that neither greater weight gain during
pregnancy or breast-feeding is found to be associated with a higher risk of breast
sagging.
Additionally, there are many health fitness magazines and
fitness trainers that propagate the claim that participation in regular upper
body exercise prevents or corrects sagging. However, there is still no evidence
of a protective effect. However, it is recommended to wear sports bra during
exercise because the constant pull of gravity and the excessive movement during
running can stretch the breast tissue possibly leading to sagging.
Having said all this, I urge you to seek a board-certified
plastic surgeon to have an in-person consultation for a breast lift. A breast
lift can raise your breasts, make them firmer, perkier, and more aesthetically
pleasing.
Hope this helps.

Thank you for your question.
Unfortunately large breast can cause the skin to stretch and the breast to drop because of the weight.
Usually the breast sag when the skin is not strong enough or the breast are too heavy or a combination of the two.
Unfortunately you cannot prevent or improve this situation without surgery...
Regards
Mr Netri