I am impressed with your bravery and courage. It is hard to face an uphill battle into the unknown. If you're like me you embrace the unknown and charge forward never to let it slow you down. Age has nothing to do with it, a heart attack is a heart attack regardless of age. I'm an emerg nurse for 10 years and I've seen a 18 y.o. with a heart attack, weirdest thing ever. It took us by surprise, due to the age, it turned he had small coronary vessels that contributed to the heart attack.
Firstly, hopefully you are being followed by a cardiologist or some other qualified professional. They need to follow your blood work and follow your heart medications as they adjust and hone in a dose that is right for you. There are various medicines but the common heart meds are beta-blockers (blood pressure and rate control) and anti-coagulants (blood thinners).
Secondly, follow a dietician or nutritionist to get your diet in check and follow a great cardiac diet. A cardiac diet is one with low fat and low sodium like in this sample cardiac diet.
Thirdly, after those steps are in place start a modified exercise regime. A cardiac exercise regime is a progressive exercise aimed at slowly ( I mean slowly) returning you to a pre-heart attack level. Start with walking a certain distance like 20 feet and work up to around the block which should take months. Buy a heart rate monitor and keep your heart rate around 60 to 70% of your maximum heart rate. If you get chest pain, sweating and SOB while exercising it means its time to taper off a bit and slow down. The exercise phase takes patience and practice. Your mind probably wants to take off but listen to your body and slow down.
Courage is defined by how much strength it takes to realize you need to slow down, you have a long life ahead, take your time.