As Dr. Harisha said it does refert size.
There are condoms available which claim to enhance the performace time. These condoms have a coating of local aneastheic, that reducest the sensation, resulting in longer time of sexual activity, but the disadvantage is it decrese the pleasure as the intensity of sensation is less.
For improving your sexual performance I suggest some simple steps that you can follow, if these do not work then as Dr. Harisha said you must meet a urologist.
Please try following suggestions.
1. At the time of sexual act, keep your mind free of any anxiety or stress.
2. If you are a smoker, please stop smoking.
3. If you drink, drink in moderation, but never before the intercourse.
4. Have long foreplay, spend time talking, cuddling kissing your partner, exxpress love, do not be in a hurry to start intercourse.
5. Make sure there is adequate privacy, sometimes lack of privacy can make you anxious, resulting in early ejaculation.
6. Do regular physical excercise , excess weigh or lack of physical fitness will affect sexual performance.
7. Make sure you are not a diabetic, also get your cholestrol checked, if there area any issues with either, get treated.
8.Yoga asanas like Bhujangasan, dhanurasan, vrishchikasaan will inprove sexual performace.
Try out these measures for few moths, if the problem persists, please see a Urologist.