Your never too old to start, whoever told you that you were too old go shoot them!
If you have determination, discipline and desire then it doesn't matter how old you are.

Firstly, learn the basics. Every boxer - from Muhammad Ali to Mike Tyson to Roy Jones to Naseem Hamed - all learned the basics BEFORE moulding it into their own personal styles. So every boxer learns the basics first for a platform to work off, a foundation. After learning the basics, you can then use your own styles.

I was pretty immature when I was boxing because all I did really was punch the pads and punch the bag, I didn't do much else apart from punch pads and bag work because I was immature. I just worked on ragged combinations all the time and putting all my efforts into each punch, that's all I really did. I know now that this was silly.

I now know that the most important things to do are roadwork and sparring, which I didn't do enough of. You need roadwork for endurance which is crucial even in the amateurs, you need to do roadwork every day for the best effect, but also for your feet (a treadmill won't have the same effect). Try to keep a good rythm on the road, don't go ragged.

As for sparring, well this is also very, very crucial. You have to be sports specific, you can do all the bag work and pad work you like, but what improves your boxing is sparring regularly. Just remember, a bag doesn't punch back at you and neither does a bag have legs to move. At the end of the day you just have to be sports specific, would you expect a sprinter to never practice sprinting? Or would you expect a soccer player to never practice soccer? No, you wouldn't. Sparring is everything in my opinion, if you do it once a week or every other day then I don't think your keeping sharp enough, you want to spar every f***ing day! If you get hurt when sparring just carry on, do not stop. Would you stop in a boxing match if you got hurt? No. If your too lazy to get up every morning to do roadwork, then what are you going to be like when your required to get up in a boxing match while your laid out in pain?

The Kronk gym in Detroit is the most successful boxing gym ever, and Manny Steward the head of the gym always made sure that his fighters sparred every day to keep sharp. Mike Tyson in his prime used to spar every day, and he was absolutely awesome (unbeatable!), but then when he fired Kevin Rooney in 1988 he stopped sparring and looked terrible. Naseem Hamed used to spar every day before he fired Brendan Ingle in 1998, and Naz was awesome Pre-98 but awful Post-98 (because he stopped sparring). Ray Robinson is arguably the best boxer that ever lived, he sparred every day.